Testosterone replacement therapy (TRT) is prescribed to men with clinically confirmed hypogonadism to restore hormone levels and alleviate symptoms such as fatigue, reduced libido, and decreased muscle mass. Whilst testosterone plays vital roles in male physiology, questions have emerged about its potential cardiovascular effects, particularly regarding heart rhythm disturbances. Can testosterone treatment cause heart arrhythmia? Recent clinical trials, including the TRAVERSE study, have identified associations between TRT and atrial fibrillation, prompting careful consideration of cardiovascular safety. Understanding the relationship between testosterone therapy and cardiac electrical activity is essential for both prescribing clinicians and patients considering or currently receiving treatment in the UK.

Understanding Testosterone Treatment and Heart Rhythm

Testosterone replacement therapy (TRT) is prescribed to men with clinically confirmed hypogonadism—a condition characterised by abnormally low testosterone levels accompanied by relevant symptoms such as reduced libido, fatigue, and decreased muscle mass. In the UK, diagnosis requires both biochemical evidence and clinical symptoms. Typically, two early-morning total testosterone measurements are needed, with levels below 8 nmol/L generally indicating hypogonadism, while 8-12 nmol/L is considered borderline and requires clinical context. Additional tests including luteinising hormone (LH), follicle-stimulating hormone (FSH), prolactin, and sex hormone binding globulin (SHBG) help determine the underlying cause and confirm the diagnosis, in accordance with guidance from the British Society for Sexual Medicine and the Society for Endocrinology.

The heart's electrical system controls rhythm through a complex network of specialised cells that generate and conduct electrical impulses. Heart arrhythmias occur when these electrical signals become irregular, causing the heart to beat too quickly (tachycardia), too slowly (bradycardia), or with an irregular pattern such as atrial fibrillation. Common symptoms include palpitations, dizziness, chest discomfort, or breathlessness, though some arrhythmias remain asymptomatic.

Testosterone exerts multiple effects on the cardiovascular system. It influences vascular tone, red blood cell production (erythropoiesis), lipid metabolism, and may affect cardiac muscle directly. These physiological actions have prompted ongoing research into whether testosterone therapy might influence heart rhythm. Understanding the relationship between TRT and cardiac electrical activity is essential for both prescribing clinicians and patients considering or currently receiving treatment.

The question of whether testosterone treatment can cause heart arrhythmia has generated considerable scientific interest and debate. Whilst testosterone plays important roles in male physiology, its cardiovascular effects—particularly regarding heart rhythm disturbances—require careful consideration when initiating or continuing therapy.

Can Testosterone Cause Heart Arrhythmia?

The relationship between testosterone therapy and heart arrhythmias remains an area of active investigation, with evidence evolving over time. While earlier studies showed mixed results, more recent research has provided important insights. The TRAVERSE trial (published in the New England Journal of Medicine, 2023) found that while testosterone therapy did not increase major adverse cardiovascular events overall, it was associated with a higher incidence of atrial fibrillation and pulmonary embolism compared to placebo.

Testosterone's mechanism of action involves binding to androgen receptors present in various tissues, including cardiac muscle. The hormone modulates cardiac ion channel activity and repolarisation, which can influence electrical conduction in the heart. Additionally, testosterone stimulates erythropoietin production, leading to increased haematocrit (red blood cell concentration), which can affect blood viscosity and cardiovascular dynamics. These physiological effects underpin the potential relationship with cardiac rhythm.

Some studies have reported associations between testosterone therapy and increased cardiovascular events, though these findings have been contested due to methodological limitations. Following safety concerns, the European Medicines Agency (EMA) and the UK's Medicines and Healthcare products Regulatory Agency (MHRA) conducted reviews (2014-2015) and concluded that when used as authorised for confirmed hypogonadism, there was no consistent evidence of increased overall cardiovascular risk, but cautionary warnings remain in product labelling.

It is important to distinguish between supraphysiological doses—such as those used in anabolic steroid abuse—and therapeutic replacement doses prescribed for hypogonadism. Anabolic steroid misuse has been associated with various cardiac complications, including arrhythmias, left ventricular hypertrophy, and sudden cardiac death. In contrast, appropriately monitored testosterone replacement aims to restore levels to the normal physiological range, which appears to carry a different risk profile. However, given the signals for atrial fibrillation in clinical trials, careful monitoring and shared decision-making are essential, particularly for men with pre-existing arrhythmias or risk factors.

Risk Factors and Cardiovascular Considerations

Certain patient characteristics may increase cardiovascular risk when considering testosterone therapy. Men with pre-existing heart conditions—including previous myocardial infarction, heart failure, or known arrhythmias—require particularly careful assessment before initiating TRT. The Medicines and Healthcare products Regulatory Agency (MHRA) advises that testosterone should be used with caution in patients with cardiovascular disease, and UK product labelling specifically mentions severe cardiac, hepatic or renal insufficiency as conditions where testosterone may cause serious complications in the form of oedema with or without congestive heart failure.

Age represents a significant consideration, as cardiovascular risk naturally increases with advancing years. Older men are more likely to have subclinical cardiac disease, atherosclerosis, or conduction system abnormalities that might theoretically interact with testosterone's cardiovascular effects. The British Society for Sexual Medicine and Society for Endocrinology guidance emphasises the importance of comprehensive cardiovascular assessment in men before commencing hormone replacement.

Other relevant risk factors include:

• Obesity and metabolic syndrome: These conditions are associated with both hypogonadism and increased cardiovascular risk, creating a complex clinical picture

• Hypertension: Testosterone may influence blood pressure through effects on vascular tone and fluid retention

• Sleep apnoea: Common in hypogonadal men and independently associated with arrhythmias; may worsen with testosterone therapy

• Polycythaemia: Testosterone-induced erythrocytosis can increase blood viscosity, potentially affecting cardiac workload

• Hyperlipidaemia: Testosterone's effects on lipid profiles remain debated, with variable impacts on cholesterol levels

Men with multiple cardiovascular risk factors require individualised assessment. The decision to prescribe testosterone should involve discussion of potential risks alongside expected benefits. Baseline cardiovascular evaluation—including blood pressure measurement, lipid profile, and consideration of electrocardiography (ECG) in patients with symptoms or risk factors—forms part of good clinical practice before initiating therapy. Patients with significant cardiac history may benefit from cardiology input to optimise their overall cardiovascular management alongside any hormone replacement.

Monitoring Heart Health During Testosterone Therapy

Appropriate monitoring during testosterone therapy is essential for detecting potential cardiovascular complications early. The British Society for Sexual Medicine recommends a structured follow-up schedule that includes both clinical assessment and laboratory investigations. Initial monitoring should occur at 3 months after starting treatment, then at 6 months, and subsequently at least annually for stable patients.

Key monitoring parameters include:

• Haematocrit and haemoglobin levels: Measured at each follow-up to detect polycythaemia. The risk varies by formulation, with higher rates typically seen with injectable preparations compared to transdermal products. Haematocrit above 0.54 (54%) typically warrants dose reduction, temporary cessation, or consideration of venesection

• Blood pressure: Checked at each visit, as testosterone may influence vascular tone and fluid retention

• Lipid profile: Assessed annually to monitor cholesterol and triglyceride levels

• Serum testosterone: Measured to ensure levels are within the mid-normal range, with timing dependent on formulation

• Prostate-specific antigen (PSA): Monitored according to age-appropriate guidelines

• Symptom review: Including specific enquiry about palpitations, chest discomfort, breathlessness, or dizziness

Electrocardiography (ECG) is not routinely required for all patients on testosterone therapy but should be considered in those with cardiovascular risk factors, pre-existing heart disease, or new cardiac symptoms. Men reporting palpitations or irregular heartbeat should undergo ECG assessment promptly. Some specialists suggest baseline ECG in men with multiple cardiovascular risk factors before initiating treatment, though this is not mandated in all UK guidelines.

Patients should be educated about potential cardiovascular symptoms and encouraged to report new or worsening concerns between scheduled appointments. Self-monitoring of symptoms—such as noting episodes of palpitations, their frequency, and associated features—can provide valuable information for clinical assessment. Regular engagement with healthcare providers ensures that any emerging cardiovascular issues are identified and managed appropriately, allowing for treatment adjustment or specialist referral when necessary.

Patients are encouraged to report suspected side effects to the Medicines and Healthcare products Regulatory Agency (MHRA) through the Yellow Card Scheme.

When to Seek Medical Advice About Heart Symptoms

Men receiving testosterone therapy should be aware of cardiac symptoms that warrant prompt medical attention. Immediate emergency assessment (calling 999 or attending A&E) is necessary if experiencing:

• Severe chest pain or pressure, particularly if radiating to the arm, jaw, or back

• Sudden onset of rapid, irregular heartbeat accompanied by breathlessness, chest pain, or loss of consciousness

• Collapse or syncope (fainting)

• Severe breathlessness at rest

• Symptoms suggestive of stroke, including facial drooping, arm weakness, or speech difficulties

These symptoms may indicate serious cardiovascular events requiring urgent intervention, regardless of whether they are related to testosterone therapy.

Non-urgent but important symptoms that should prompt contact with your GP or prescribing clinician include:

• New or persistent palpitations (awareness of heartbeat)

• Episodes of dizziness or light-headedness

• Reduced exercise tolerance or breathlessness on exertion

• Swelling of ankles or legs

• Unusual fatigue or weakness

Your GP can arrange appropriate investigations, including ECG, blood tests, or referral to cardiology if indicated. It is important to mention that you are receiving testosterone therapy, as this forms part of your medical history relevant to cardiovascular assessment. If you're unsure about the urgency of symptoms, NHS 111 can provide guidance.

Regular communication with your prescribing clinician ensures optimal safety monitoring. Do not discontinue testosterone therapy abruptly without medical advice, as this should be done under supervision. If cardiovascular concerns arise, your doctor will assess whether treatment modification, additional investigation, or specialist input is required. Many cardiac symptoms have multiple potential causes unrelated to testosterone therapy, and proper evaluation will determine the underlying issue and appropriate management. Maintaining scheduled follow-up appointments and adhering to recommended monitoring protocols provides the best framework for safe, effective testosterone replacement therapy whilst safeguarding cardiovascular health.

If you suspect you're experiencing side effects from testosterone treatment, report these through the MHRA Yellow Card Scheme, which helps monitor the safety of medicines in the UK.

Frequently Asked Questions