Obesity medication, heart disease and atrial fibrillation

Semaglutide (Wegovy) and tirzepatide (Mounjaro), the obesity medicines given as a once-weekly injection, have also been studied in people with heart disease. In people without diabetes who had had a heart attack or stroke or who had peripheral arterial disease, semaglutide injections reduced the combined risk of heart attack, stroke and cardiovascular death. In patients with obesity and heart failure with preserved ejection fraction, both medicines reduced heart failure symptoms (1, 2, 3). A meta-analysis published in October 2026 found that new cases of atrial fibrillation were less common in people on semaglutide injections (4). However, a review of earlier meta-analyses rated the certainty of the evidence for this association as low (6).

At the same time, these medicines increase heart rate by an average of 2-3 beats per minute (1, 5). In people with heart disease, the medicines they already take also have to be considered: anticoagulants, diuretics and blood pressure medicines. The findings on atrial fibrillation apply to semaglutide injections, not to the tablets. A doctor chooses the obesity medicine, and anyone with heart disease should also discuss the treatment plan with their cardiologist.

In brief

• In an analysis of 94 trials in people with type 2 diabetes or obesity, new cases of atrial fibrillation were about 18% less common in people on semaglutide injections than in people on placebo. The finding applies to the injections, and the certainty of such findings has been rated as low (4, 6).
• In people with obesity and heart failure with preserved ejection fraction, semaglutide reduced heart failure symptoms, such as breathlessness and tiredness, and improved the ability to carry out everyday activities. Over about 2 years, tirzepatide reduced the number of episodes of worsening heart failure (2, 3).
• Semaglutide and tirzepatide increase resting heart rate by an average of 2-3 beats per minute, and in some people by much more. Palpitations or a fast heartbeat at rest that does not go away need to be reported to a doctor (1, 5, 7).
• Before starting treatment, you need to discuss anticoagulants, diuretics and blood pressure medicines with the doctor. People taking acenocoumarol or warfarin have their INR (a measure of how well the blood clots) checked more often after starting semaglutide (1).

Does semaglutide reduce the risk of atrial fibrillation?

Possibly, but the evidence is weak. In a meta-analysis from October 2026, semaglutide injections came out best on this measure among the medicines in this group, with fewer new cases of atrial fibrillation than on placebo (4). However, a review of earlier meta-analyses on the subject found them to be of low reliability (6).

Atrial fibrillation is a heart rhythm disorder in which the heart beats irregularly and usually faster than normal. It can cause palpitations, tiredness, breathlessness and dizziness (8). In people with obesity, the risk of atrial fibrillation is about 50% higher than in people with a healthy body weight (9).

The authors of the network meta-analysis pooled 94 randomised trials with a total of 155,989 people with type 2 diabetes or obesity. In these trials, 12 medicines (GLP-1 receptor agonists and similar medicines such as tirzepatide) were compared with placebo or with each other. A network meta-analysis also makes it possible to compare medicines that have never been tested against each other in the same trial. In people on semaglutide injections, new cases of atrial fibrillation were about 18% less common than in people on placebo. The result was borderline statistically significant: according to the calculations, the true difference could have been as small as 1%. By contrast, dulaglutide, a medicine from the same group used to treat diabetes, was associated with more frequent atrial fibrillation (4).

This result needs to be read with caution. A review of 10 earlier meta-analyses on the same subject found that they largely rely on the same trials, and rated as low the certainty of the finding that atrial fibrillation is less common. The effect was clearer in people with type 2 diabetes than in people with obesity alone. The authors of the review stress the need for trials in which heart rhythm is checked according to a set schedule and every case of atrial fibrillation is confirmed by an independent committee (6). Only such trials can settle whether semaglutide protects against this arrhythmia. Semaglutide is not licensed to prevent atrial fibrillation (1).

Why doesn't the atrial fibrillation finding apply to semaglutide tablets?

The authors of the meta-analysis report the result separately for semaglutide injections, and their conclusion applies only to this form (4). Only about 1-2% of the semaglutide in a tablet reaches the blood, which is why the tablet contains 25 mg of the medicine and the injection 2.4 mg. The amount absorbed also varies from person to person, and even in the same person from day to day (1). The result for the injections therefore cannot be applied to Wegovy tablets. The differences between the two forms are described in our article on semaglutide tablets and injections.

Does tirzepatide increase the risk of atrial fibrillation?

In the network meta-analysis, tirzepatide did less well on this measure than semaglutide injections (4). However, in a separate analysis of 10 trials in which 6,515 people with overweight or obesity received tirzepatide or placebo, the difference in the frequency of atrial fibrillation between the groups was not statistically significant. More heart rhythm disorders overall were reported in people on tirzepatide, but there were few such events, and the authors advise caution in interpreting this result (10). In the trials on which its approval for treating obesity was based, heart rhythm and conduction disorders were reported in 3.3-3.7% of people on tirzepatide and 3.6% of people on placebo (5).

Does losing weight reduce atrial fibrillation symptoms?

Yes. The European Society of Cardiology (ESC) recommends that people with atrial fibrillation who are overweight or have obesity lose at least 10% of their body weight. The aim is to ease symptoms and reduce the time the heart spends in atrial fibrillation (11). According to Polish guidelines, regular physical activity and better fitness also improve the outlook in atrial fibrillation (9). Obesity medication is one way to achieve this amount of weight loss. It is always used together with changes to diet and more physical activity.

The results of several studies suggest that semaglutide reduces the risk of atrial fibrillation coming back after ablation, a procedure intended to eliminate the source of the arrhythmia in the heart. The certainty of this evidence has been rated as very low (6).

Can you take obesity medication if you have heart failure with preserved ejection fraction?

Semaglutide and tirzepatide injections have been tested in this type of heart failure in separate trials in people with obesity. Both medicines reduced heart failure symptoms and limitations in everyday activities, and in the tirzepatide trial there were also fewer episodes of worsening heart failure (2, 3, 12). Semaglutide is not recommended in class IV, the most severe class of heart failure, because data on its safety in these patients are lacking (1).

Ejection fraction shows what proportion of the blood in the left ventricle of the heart is pumped out with each contraction. It is measured with an echocardiogram (heart ultrasound). In heart failure with preserved ejection fraction, the heart contracts normally, but the left ventricle is stiffer and does not fill with blood as well. Obesity is more strongly linked to this type of heart failure than to the type with reduced ejection fraction. Breathlessness, reduced exercise tolerance and swollen legs are easy to put down to obesity alone, which is why heart failure is diagnosed later in people with obesity (9).

What did semaglutide trials in heart failure show?

In the STEP-HFpEF trial, 529 people with heart failure with preserved ejection fraction and a BMI of at least 30, without diabetes, received semaglutide 2.4 mg once a week or placebo for a year. Symptoms and limitations in daily life were assessed with the KCCQ questionnaire on a scale of 0 to 100 points, where a higher score means fewer symptoms. The score improved by 16.6 points in the semaglutide group and by 8.7 points in the placebo group. Body weight fell by an average of 13.3% in people treated with semaglutide and by 2.6% in the placebo group. The distance participants walked in 6 minutes increased by 21.5 m on semaglutide and by 1.2 m on placebo. Serious adverse events were reported in 13.3% of people on semaglutide and 26.7% of people in the placebo group (2).

In the STEP-HFpEF DM trial, the 616 participants with the same type of heart failure also had type 2 diabetes. The KCCQ score improved by 13.7 points in the semaglutide group and by 6.4 points in the placebo group, and body weight fell by 9.8% and 3.4% respectively (12). Both trials were funded by the manufacturer of the medicine.

A pooled analysis of four semaglutide trials, carried out after they had ended, included 3,743 people with heart failure with preserved or mildly reduced ejection fraction. Cardiovascular death or worsening heart failure requiring a hospital stay or an urgent visit occurred in 5.4% of people on semaglutide and 7.5% of people in the placebo group. There were fewer episodes of worsening heart failure, but the number of cardiovascular deaths did not differ significantly between the groups (13).

What did the tirzepatide trial in heart failure with preserved ejection fraction show?

In the SUMMIT trial, 731 adults with obesity and heart failure with an ejection fraction of at least 50% received tirzepatide at doses of up to 15 mg once a week or placebo. Follow-up usually lasted about 2 years. Almost half of the participants also had type 2 diabetes. Most continued to take their existing heart failure medicines, and almost three quarters of participants were taking diuretics (3, 5).

Cardiovascular death or worsening heart failure occurred in 9.9% of people on tirzepatide and 15.3% of people in the placebo group. Worsening heart failure was defined as a hospital stay, an urgent visit or the need to step up treatment with oral diuretics because of heart failure. The difference was driven by fewer episodes of worsening heart failure in the tirzepatide group (8.0% compared with 14.2%). There were few cardiovascular deaths in either group, slightly more in the tirzepatide group, but the difference was not statistically significant. The trial therefore does not settle how tirzepatide affects the risk of death (3, 5).

After a year, the KCCQ score had improved by 19.5 points in the tirzepatide group and by 12.7 points in the placebo group. Side effects, mainly gastrointestinal, led 6.3% of people on tirzepatide and 1.4% of people in the placebo group to stop treatment (3).

What is known about obesity medication in heart failure with reduced ejection fraction?

There are fewer data on obesity medication for this type of heart failure, because the STEP-HFpEF and SUMMIT trials included only people with preserved ejection fraction. With reduced ejection fraction, the heart contracts less forcefully. Some of the available data come from the SELECT trial in people with heart or blood vessel disease, in which 1,347 of the 17,604 participants had heart failure with reduced ejection fraction. In this group, the combined number of heart attacks, strokes and cardiovascular deaths was lower in people on semaglutide than in the placebo group. There were also fewer deaths and hospital admissions due to heart failure, but in this group the difference was not statistically significant (14).

Like semaglutide, liraglutide is not recommended in class IV on the NYHA scale, the most severe class of heart failure (7). The Polish guidelines also point out that in some patients with advanced heart failure, low body weight is linked to a worse outlook. This is why weight loss is not automatically recommended for everyone with heart failure who is overweight, and the outlook is better in patients who are physically fit and have kept their muscle mass (9). Whether and how someone with heart failure should lose weight is decided by the cardiologist together with the doctor managing the obesity treatment.

Which obesity medicine is used after a heart attack or stroke?

In people who have had a heart attack or stroke or who have peripheral arterial disease, the Polish guidelines name once-weekly semaglutide 2.4 mg injections as the first option to consider (9). In a large trial in such people without diabetes, semaglutide reduced the combined risk of heart attack, stroke and cardiovascular death.

In the SELECT trial, 17,604 people with heart or blood vessel disease and a BMI of at least 27, without diabetes, received semaglutide injections or placebo in addition to their usual treatment. The combined risk of heart attack, stroke and cardiovascular death was 20% lower in the semaglutide group (1). We write more about the SELECT trial in our article on semaglutide tablets and injections. No similar trial has been carried out for Wegovy 25 mg tablets (1).

Tirzepatide was compared with dulaglutide, a GLP-1 receptor agonist, in 13,299 people with type 2 diabetes and heart or blood vessel disease. The combined risk of heart attack, stroke and cardiovascular death was not higher in the tirzepatide group than in the dulaglutide group, but tirzepatide did not prove more effective either (5). A trial testing whether tirzepatide reduces the number of heart attacks, strokes and deaths in people with obesity without diabetes is still under way. It is scheduled to finish in 2027 (15).

How much do obesity medicines increase heart rate?

Semaglutide, tirzepatide and liraglutide increase resting heart rate by an average of 2-3 beats per minute. In some people, heart rate rises more markedly, which is why it needs to be monitored in people with heart disease (1, 5, 7).

A fast heartbeat reported as a side effect is less common than a rise in measured heart rate: it is uncommon with semaglutide, meaning it may affect up to 1 in 100 people, and common with tirzepatide, meaning it may affect up to 1 in 10 people (1, 5). The long-term significance of the average rise in heart rate on liraglutide has not been established. The manufacturer of this medicine recommends checking heart rate regularly and stopping treatment if resting heart rate remains clearly raised (7).

Naltrexone/bupropion in heart disease

Naltrexone/bupropion tablets (Mysimba) can raise blood pressure and heart rate. Blood pressure and heart rate are measured before treatment starts and regularly during it, and if they rise markedly and stay raised, the medicine is stopped. The medicine must not be used in uncontrolled high blood pressure. Data are lacking on its safety in people who have recently had a heart attack, have unstable heart disease or have NYHA class III or IV heart failure. The manufacturer advises caution in active coronary heart disease and in diseases of the blood vessels in the brain (16).

What should you discuss with your cardiologist before starting obesity treatment?

Before starting obesity treatment, talk to your cardiologist or the doctor treating your heart condition. Discuss the type of heart disease you have, your heart rate, anticoagulants, diuretics and blood pressure medicines, and any planned procedures.

• Type of heart failure. Trials of obesity medication in heart failure mainly included people with preserved ejection fraction, so the doctor needs the result of your most recent echocardiogram.
• Heart rate and rhythm. If you have atrial fibrillation, it helps to know your usual resting heart rate before treatment and to agree with your cardiologist how often to measure it after starting the obesity medicine and after each dose increase.
• Anticoagulants. If you take acenocoumarol or warfarin, the doctor may order more frequent INR tests.
• Diuretics and fluid restriction. Agree in advance what to do if you have vomiting or diarrhoea.
• Blood pressure medicines. As your weight goes down, your blood pressure may fall, and the doctor then adjusts the doses of your medicines.
• Procedures under general anaesthesia or deep sedation. You need to tell the doctor and the anaesthetist about the obesity medicine beforehand, because semaglutide and tirzepatide slow down stomach emptying and increase the risk of inhaling stomach contents (aspiration). This also applies to heart procedures, such as electrical cardioversion, if they are done under this kind of anaesthesia (1, 5).

Taking anticoagulants with semaglutide or tirzepatide

After semaglutide is started, the manufacturer recommends frequent INR tests in people taking warfarin or other medicines from the same group, including acenocoumarol. INR is a measure of blood clotting used to set the dose of these medicines. Cases of reduced INR have been described in patients taking acenocoumarol together with semaglutide (1). With tirzepatide, the manufacturer recommends monitoring people taking warfarin, digoxin and other medicines for which a small change in blood level matters a great deal, especially at the start of treatment and after a dose increase (5). Anyone taking an anticoagulant from a different group, such as apixaban, dabigatran or rivaroxaban, must also tell the doctor prescribing the obesity medicine about it.

You take a semaglutide tablet on an empty stomach and then wait at least 30 minutes before taking any other oral medicines (1). How to plan your morning medicines is described in our article on combining semaglutide tablets with other medicines.

Diuretics, fluids and blood pressure during obesity treatment

Nausea, vomiting and diarrhoea are common at the start of treatment with semaglutide and tirzepatide. Dehydration can then impair kidney function, which is why the manufacturers recommend drinking more fluids (1, 5). However, some people with heart failure take diuretics and have been told to limit how much they drink. Before starting obesity treatment, you need to agree with your cardiologist how much to drink and what to do about your diuretics if you develop vomiting or diarrhoea. For ways to ease nausea and diarrhoea, see our article on side effects of obesity medication.

Losing 5-15% of body weight can lower blood pressure (9). Low blood pressure is common in people taking tirzepatide and uncommon with semaglutide. Dizziness or light-headedness when standing up may mean that your blood pressure has dropped too far (1, 5). The doctor then changes the doses of your blood pressure medicines and diuretics. You should not reduce or stop them yourself.

When do heart symptoms during obesity treatment need urgent help?

A fast or irregular heartbeat with chest pain, breathlessness, fainting or severe dizziness needs immediate medical help; do not wait until you can contact your clinic (8).

Symptoms that need immediate help in someone with heart disease

• a fast or irregular heartbeat together with chest pain or tightness, breathlessness, sweating, nausea, dizziness or fainting (8)
• a fast or irregular heartbeat together with weakness or numbness on one side of the face or body, difficulty speaking, sudden worsening of vision or confusion (8)
• very severe breathlessness that leaves you unable to speak, blue or grey lips, loss of consciousness (17)
• difficulty breathing, sudden swelling of the face, throat, arms or legs, dizziness and a fast heartbeat after taking the medicine, because these may mean a severe allergic reaction (1, 5)

Symptoms that mean you should contact a doctor urgently if you have heart disease

• breathlessness during everyday activities or when lying down, a cough at night (17)
• sudden weight gain or increasing swelling of the feet, ankles, legs or abdomen (17)
• palpitations or a fast heartbeat at rest that does not go away or gets worse (7, 8)
• vomiting or diarrhoea that makes it impossible to replace lost fluids, passing little urine, and dizziness when standing up, because dehydration can damage the kidneys (1, 5)

In someone with heart failure, sudden weight gain may mean that the body is retaining fluid (17). If you weigh yourself regularly during obesity treatment and notice such a rise, you should not put it down to the medicine having stopped working; report it to your doctor instead.

Treating obesity with medication in the Nasz Gabinet programme if you have heart disease

In the obesity treatment programme at Nasz Gabinet, the doctor checks at a video consultation whether an adult patient meets the Polish Society for the Treatment of Obesity (PTLO) criteria for drug treatment, and chooses a medicine. The doctor can prescribe semaglutide as an injection, semaglutide as a tablet or tirzepatide; semaglutide injections remain the first choice in the programme. The doctor issues an e-prescription and assesses the progress of treatment every month based on the measurements the patient records in the app. The medicine is bought separately at a pharmacy. The programme lasts 12 months and includes video consultations with a doctor and a psychologist, but it does not replace care from a cardiologist. For the initial consultation, prepare a list of your heart medicines with their doses, the result of your most recent echocardiogram and your cardiologist's recommendations. The criteria a doctor uses to decide whether you are eligible for treatment are described in our article on eligibility for obesity medication.

Frequently asked questions

Can Ozempic or Wegovy cause atrial fibrillation?

In a meta-analysis of trials of semaglutide injections, new cases of atrial fibrillation were slightly less common in people on treatment than in people on placebo (4). The certainty of this evidence is low, however (6). Ozempic and Wegovy injections both contain semaglutide; Ozempic is licensed for treating type 2 diabetes, and Wegovy for treating obesity. If you have palpitations or an irregular heartbeat during treatment, you need to tell your doctor, who will establish the cause.

Can you take Mounjaro if you have atrial fibrillation?

The summary of product characteristics (SmPC) for Mounjaro does not list atrial fibrillation among its contraindications or warnings (5). In an analysis of trials in people with obesity, atrial fibrillation was not significantly more common with tirzepatide than with placebo (10). However, tirzepatide increases heart rate by an average of 3 beats per minute, and on the 15 mg dose, 6.3% of people had a marked, sustained rise in heart rate, compared with 1.2% on placebo (5). This is why, in someone with atrial fibrillation, the doctor takes into account how the arrhythmia is being treated and what the cardiologist recommends before deciding on tirzepatide.

Do Wegovy tablets protect the heart as the injections do?

This is not known. The SELECT trial and the trials in people with heart failure looked at semaglutide injections, and no similar trial has been carried out for Wegovy 25 mg tablets (1). The meta-analysis finding on atrial fibrillation also applies to the injections (4). According to the Polish guidelines, semaglutide 2.4 mg injections are the first option to consider in people who have had a heart attack or stroke or who have peripheral arterial disease (9).

Can you stop your heart medicines during obesity treatment as your weight goes down?

Not on your own. In the SELECT and SUMMIT trials, the obesity medicine was added to the heart medicines participants were already taking (1, 5). When your weight and blood pressure change, the doctor may change the doses of your blood pressure medicines or diuretics.

Sources

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