The cardiovascular question around testosterone is the most complicated in men's health. On one hand, low testosterone is associated with poor cardiovascular outcomes in observational studies. On the other hand, some trials suggested TRT might increase cardiac risk. The truth, as usual, is more nuanced than either extreme position.
Let me walk you through the evidence, what changed in 2023, and what actually matters for your decision.
The Observational Picture: Association Doesn't Equal Causation
Men with low testosterone have higher rates of heart disease, heart attacks, and stroke. This is well-established in observational data—thousands of men followed over years show this pattern.
The question: does low testosterone cause poor cardiovascular outcomes, or does something else (obesity, poor fitness, metabolic dysfunction, smoking) cause both low testosterone and heart disease?
Probably both. Low testosterone is associated with metabolic dysfunction, reduced exercise capacity, and poor physical health—all independent cardiac risk factors. It's not clear how much of the association is testosterone itself versus these confounding factors.
This is why observational data alone can't answer whether TRT helps the heart. You need an RCT.
The Basaria 2010 Fear: The Context Matters
In 2010, Shalender Basaria published a small study of 209 men (mostly elderly, many with chronic illness) who received testosterone or placebo. The TRT group had numerically more cardiovascular events (MACE—major adverse cardiovascular events: heart attacks, strokes). The study was terminated early.
This study went viral. It became the justification for TRT caution. One problem: the men studied were frail, elderly, mostly with existing cardiovascular disease. The generalisability to a healthy 45-year-old man starting TRT was questionable.
Still, the concern was valid. You can't dismiss a safety signal, even in a small, non-representative sample.
The TRAVERSE Trial 2023: The Game-Changer
The TRial of Cardiovascular Events Reduction with Testosterone (TRAVERSE) was designed to answer the question properly. Published in 2023, it's the largest RCT of TRT and cardiovascular outcomes:
- ~5,000 men, average age 63
- Testosterone gel versus placebo
- Three-year follow-up
- Primary outcome: MACE (heart attack, stroke, cardiovascular death)
Key findings:
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No increase in MACE. TRT did not increase the risk of heart attack, stroke, or cardiovascular death compared to placebo. The primary outcome was similar between groups.
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Non-fatal arrhythmia increased. Men on TRT had more episodes of atrial fibrillation and other non-fatal arrhythmias. This is worth noting—not life-threatening, but annoying and potentially concerning.
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Pulmonary embolism increased. Men on TRT had a higher rate of blood clots in the lungs. Again, not massive numbers, but statistically significant and worth taking seriously.
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Haematocrit rose on TRT. This is the mechanism for the thrombotic risk. Testosterone stimulates red blood cell production, raising haematocrit. More RBCs = thicker blood = higher clot risk.
What This Means: The Balanced View
TRAVERSE is good news and bad news:
Good news: TRT doesn't cause heart attacks or strokes in appropriately screened men. The fear that TRT will give you a heart attack is overdone. Basaria's warning doesn't generalise to healthy men.
Bad news: TRT increases the risk of non-fatal but serious complications—arrhythmias and clots. These are real considerations, not edge cases.
Practical implications: TRT appears cardiovascularly neutral to slightly negative in terms of thrombotic risk. It doesn't protect your heart (despite some claims that raising testosterone will improve cardiac function). And you need to manage the clot and arrhythmia risk actively.
Haematocrit and Blood Viscosity: The Mechanism
Here's what's happening: testosterone increases erythropoietin (EPO) production in the kidneys, which stimulates red blood cell production. More RBCs means higher haematocrit (the percentage of blood that's RBCs).
At normal haematocrit (~40-50%), this is fine. But if haematocrit rises above 54-55%, blood becomes visibly thicker. Viscous blood increases clot risk and can reduce oxygen delivery paradoxically (thickened fluid moves poorly through capillaries).
How to manage this:
- Get haematocrit checked at 3 months after starting TRT, then every 6-12 months
- If haematocrit rises above 54%, you have options:
- Reduce TRT dose
- Increase training volume (exercise reduces haematocrit slightly)
- Donate blood (remove a unit of blood every 2-3 months; straightforward, though check with your clinic)
- Switch to a lower-dose formulation or frequency
Most men stay in acceptable range. Some (maybe 10-15%) need intervention. But you're not stuck if your haematocrit rises—you can actively manage it.
Blood Pressure on TRT
Testosterone modestly raises blood pressure in some men. The effect is typically small (5-10 mmHg) but real. If you have baseline hypertension, you might see worsening.
Practical: Get a baseline BP before starting TRT, monitor it at 3 months and 6 months, then annually. If BP rises significantly, discuss with your doctor whether dose reduction or added anti-hypertensive therapy is appropriate.
Atrial Fibrillation: The Arrhythmia Risk
TRAVERSE found increased non-fatal atrial fibrillation (AFib) in the TRT group. AFib is irregular heartbeat, sometimes asymptomatic, sometimes causing palpitations, shortness of breath, or fatigue.
Why? Testosterone likely increases atrial electrical irritability and inflammation. The mechanism isn't fully clear.
Risk factors for AFib on TRT:
- Pre-existing AFib or arrhythmia history
- Older age
- Higher doses of testosterone
- Rapid dose escalation
What to watch for:
- Palpitations (feeling your heart beating irregularly)
- Shortness of breath
- Fatigue or exercise intolerance
If these develop, get an ECG. AFib isn't an emergency, but it requires monitoring. Some men tolerate it fine; others need to come off TRT or reduce dose.
Who Should Avoid TRT (Cardiovascular Grounds)
- Men with uncontrolled hypertension (BP >160/100)
- Men with active AFib (stable, treated AFib is more debatable, but discuss with cardiologist)
- Men with a recent heart attack or stroke (within the last 3-6 months)
- Men with congestive heart failure (ejection fraction <40%)
- Men with a strong family history of sudden cardiac death (assess individually with cardiologist)
The Metabolic Angle: Low T and Cardiovascular Risk
Here's the unresolved question: if low testosterone contributes to cardiovascular disease risk (via poor metabolic health, obesity, reduced exercise capacity), does raising testosterone with TRT reduce that risk?
TRAVERSE doesn't answer this definitively. The study didn't show that TRT improves cardiac outcomes, only that it doesn't worsen them in the primary sense (MACE). The increased arrhythmia and clot risk offsets any potential benefit.
In other words: TRT is cardiovascularly neutral to slightly negative. Don't do it thinking you're protecting your heart. Do it (if indicated) knowing that you're accepting a small thrombotic risk in exchange for the benefits to muscle, bone, mood, and sexual function.
What to Do Before Starting TRT
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Baseline cardiovascular assessment:
- Blood pressure check
- ECG (resting electrocardiogram)
- If age >50 or significant risk factors, consider stress test or lipid panel
- Haematocrit baseline
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Risk factor inventory:
- Smoking? Stop before TRT.
- Hypertension? Get it controlled first.
- Obesity? Weight loss should come before or alongside TRT, not instead of it.
- Family history of early MI or stroke? Disclose to your doctor.
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Monitoring protocol (non-negotiable):
- BP at 3 months, 6 months, annually
- Haematocrit at 3 months, 6 months, then annually (or more frequently if trending up)
- Ask your doctor about arrhythmia screening (symptom checklist, maybe ECG at baseline and 1 year)
The Bottom Line
Testosterone replacement doesn't cause heart attacks or strokes in healthy, appropriately screened men. That's the TRAVERSE headline, and it's true.
But TRT does increase non-fatal arrhythmia and clot risk, probably via haematocrit elevation and direct electrical effects on the heart. These aren't deal-breakers, but they're real.
Don't do TRT thinking it's cardio-protective. Do it (if indicated by low symptoms and lab values) knowing that you're taking on a small additional risk in exchange for other benefits, and you're committing to regular monitoring to catch problems early.
Cardiovascular health matters more than testosterone levels. If you have the choice between weight loss, exercise, blood pressure control, and smoking cessation versus TRT, choose the former. If you have genuinely low testosterone and you've optimised those basics, then TRT is a reasonable option with known risks and benefits.
Bottom line: TRT is cardiovascularly neutral to slightly risky (clot/arrhythmia). Monitor haematocrit closely. Commit to the monitoring protocol before you start.