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Heart Matters: Reducing Cardiac event risk in the swim leg of triathlons

How can you eliminate the risk of a cardiac event during the swim leg in a triathlon?

Having an echocardiogram doesn’t always need to be when you experience discomfort or feeling poorly. If you want to participate in endurance sport, I suggest having regular check-ups to make sure you know that your heart can handle the demand you are asking from it.

Magda Nieuwoudt, Head Trainer at Trivium and professional triathlete

Magda Nieuwoudt exiting the water stage of a triathlon competition

When you ask your heart to handle stress for more than 8+ hours during events like Ironman or 4+ for half ironman distances, it is crucial to know that you have a healthy heart. Athletes sometimes neglect the proper recovery from anaerobic workloads and not taking enough rest after or during an illness. This can lead to potential permanent heart muscle scarring and a serious cardiac event. Athletes are known for having a strong mind, but it sometimes can work against us. Like training when you are not feeling well and not going easier on sessions when your body is tired – the stress load is just too much.

One would think training for an aerobic event is safe but triathlons and ultra marathons are known for casualties during races and mostly because of heart failure.

Statistics have shown that casualties from endurance races for last year (2022) were 19 deaths - 87% were during the swim leg – of which were mostly heart attacks and a few drownings. Since 1986, there have been 195 deaths in total - 144 (73.8%) during the swim, 26 (13%) during the bike, 9 (4.6%) on the run and 14 after the race. 90% of these cases were heart failure related, and the other causes were dehydration and hypoglycaemia.

Why does the occurrence of heart failure happen mostly during the swim leg at the beginning of the race and not during the bike or run when one would think the load on the heart is really taking a beating? Studies have been done over the years on divers and triathletes and they have concluded that this life-threatening condition can be known as swimming-induced pulmonary edema (SIPE).

SIPE is characterized by acute onset of dyspnoea, cough and or expectoration of frothy sputum and is associated with water immersion especially colder temperatures. Athletes who experience this during swimming need to be evacuated from the swim and treated with extra oxygen. What makes the investigation and studying difficult is that most athletes who experience mild symptoms of SIPE don’t go to the medical tent and only the severe cases are being documented. Also, not all fatal cases have post-mortem results


Doctor Moon investigated SIPE and documented a few articles on the matter. He

investigated 23 triathlon deaths that occurred during the swim leg and found that the majority of the 23 athletes had left ventricle hypertrophy (LVH). Now this is also vague as athletes are commonly known to have a thicker heart muscle wall.

Other known causes are because of exertion, but the onset of symptoms in SIPE does not correlate to the duration of exertion as in many cases seem to happen soon after entering the water. So, it seems like the immersion of water could be a factor. Other risk factors like cold water force the venous pooling of blood (blood without oxygen) to the central part of our bodies which in turn increases cardiac preload (preload refers to the amount of blood already in the main pumping chambers when you're ready to pump it out). In contrast to the cold, in warmer conditions, over hydration exacerbates central venous pooling due to increase venous blood plasma. The tight fitting of wetsuits and the external compression from peripheral compression of veins and limbs, lead to central venous

pooling and again increases cardiac preload.

Magda Nieuwoudt correctly fitting a wetsuit for the water stage of a triathlon

Although the exact pathology of SIPE cannot be stated there are a few theories of what the cause can be, and I have witnessed a few of these exact examples happening to some of my athletes.

The main take away is that when immersed in water a redistribution of blood from extremities lead to central pooling. It also enhances further with vasoconstriction of a tight wetsuit or putting on your wetsuit too early or standing in the heat – this all can/will lead to increase in blood plasma. When getting into cold water this all leads to an increase in cardiac preload and increases the left atrial pressure. The demand for higher cardiac output because of the intensity from the swimming you want to do will lead to higher pulmonary artery pressure. The hydrostatic pressure leads to pulmonary oedema.

Most wetsuits are good, and this is not a blog to scare you from buying a wetsuit or doing a triathlon, but just a few crucial tips on how to play it safe from my own personal experience.

Avoid putting your wetsuit on too early before the race. I see a lot of athletes putting on their wetsuits early in the morning, in their hotel room walking to transition fully suited up, walking in their wetsuits all morning to only stand still in the starting block for 30- 45 min (this is bad especially if it is in a hot environment). Having your wetsuit on also means you are not able to do a good / proper warm-up and end up waiting, standing dead still in the suits for your turn to run into the water.

Athletes with left ventricle hypertrophy (thickening of the heart muscle) are less able to cope with cardiac preload. And those with conditions that increase the afterload (the force against which the heart must contract to eject the blood) like hypertension, obstructive cardiomyopathy or significant valve disease would be expected to have higher pressures in the left atrium at a given level of preload and would also be at risk for SIPE.

Magda Nieuwoudt fastening her wetsuit before a triathlon

The main take away from this blog is that with external attributes to open water swimming like compression from wetsuits, cold water immersion, higher blood volume due to heat, increase central and cardiac pooling. Because you are exerting high intensity exercise, your cardiac output also increases which causes a massive load on the working of the heart. If you have any underlying heart condition you may be at a higher risk of pulmonary oedema which can lead to fatality.

Most of the cardiac markers might be unknown to the general athlete and therefore I strongly suggest:

  • Get regular check-ups for any risk or concerns to your heart!!

  • Don’t fully zip-up your wetsuit before the race. Have it waist height and then 10-15 minutes before start fully zipped-up.

  • Make sure you have the right fitted wetsuit and it is not too compressed around the legs and hip area.

  • Always do a proper warm up before the swim. Do a short 10-15 min run so your blood circulation goes through the whole body waking up all the systems needed to race.

  • Never train when you are not feeling well.

  • Manage your stress load from work, training, and family.

  • Always make time to sleep enough when training for an endurance event.

  • Visiting a cardiologist regularly should become part of your yearly routine as an athlete.

Like caring for our skeletal muscle, we should care for our cardiac muscle. Your Heart Scan ( offers a walk-in assistance without the referral of a doctor needed. Contact them for more assistance and make sure you get on the starting line with no regrets or concerns race ready!


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