> I wonder how much of this is pre-existing heart conditions that went undiagnosed versus running _causing_ heart damage.

The sample size might be too small, but I'd love to see a comparison of heart-failure events among ultra runners to other very intense exercise.

Conditions like Marfan Syndrome are obvious candidates for these deaths: it's often undiagnosed, it significantly increases risk for sudden heart failures like aortic dissection (especially in younger people), and it produces a progressive risk with intense exercise (by weakening heart tissues which then stretch under stress). Which, oddly, is both pre-existing and exercise-induced; running wouldn't do the same thing without the condition, but a sufferer who didn't run as hard might never have a problem.

Directly attributing the problem to conditions like that is probably impossible; there are a bunch of them and there's no guarantee they'll be diagnosed or even caught at autopsy. But a cross-sport comparison might turn up interesting data - breath-restricting sports like swimming and scuba diving are higher risk than running.

> This is surprising to me... I've run almost 5000 miles and 6 marathons so far and this has not been my experience.

Do you track your resting heart rate on the days after running a marathon? It's been pretty consistent to me. If I sustain near max exertion for multiple hours, it takes at least a few days to feel normal again, and resting heart rate seems to be a very good indicator of the overall stress of the exertion. Obviously my RHR is dropping over time. These are temporary variations.

I've been reading this thread and I'm curious if you've had any cardiac checkups done.

I had a friend who was very healthy and fit but, like you, experienced elevated heart rate (and some loss of energy) for a few days after hard exercise days. Turns out, he had a partial blockage in a cardiac blood vessel. It was not blocked enough to be noticeable under normal workloads. But under hard work loads, part of his heart did not get enough oxygen and experienced damage. Eventually he experienced a heart attack, which is when it was caught and stented. Every other vessel was clear... it was just one of those flukes.

Who knows if you have the same issue, but I would suggest it's worth getting checked out.

Yeah I'm feeling a little unsure myself after reading these replies... I had a checkup very recently and got the all clear... The most recent incident I was referring to (I hiked up 5000 feet in a couple hours and ran the descent) caused severe DOMS, and I think the elevated RHR may have been due to muscle damage in my legs. I was probably not physically prepared for that large of a running descent. But I'll keep an eye on it.

Yeah I peek at my heart rate graphs daily, but not with any kind of scientific rigor

I just love marathon running and I'd hate for it to be hurting me long term...

It's not as much about your "experience". IIRC there was scarring in heart tissue after running a marathon distance in a large majority of runners independent of training. This could plausibly impede blood flow if the heart's fitness dropped back to "normal" (i.e. in old age). That said, I still do distance running.

"An ultra-marathon can also lead to changes in biomarkers indicating a pathological process in specific organs or organ systems such as skeletal muscles, heart, liver, kidney, immune and endocrine system. These changes are usually temporary, depending on intensity and duration of the performance, and usually normalize after the race. In longer ultra-marathons, ~50–60% of the participants experience musculoskeletal problems. The most common injuries in ultra-marathoners involve the lower limb, such as the ankle and the knee. An ultra-marathon can lead to an increase in creatine-kinase to values of 100,000–200,000 U/l depending upon the fitness level of the athlete and the length of the race. Furthermore, an ultra-marathon can lead to changes in the heart as shown by changes in cardiac biomarkers, electro- and echocardiography. Ultra-marathoners often suffer from digestive problems and gastrointestinal bleeding after an ultra-marathon is not uncommon. Liver enzymes can also considerably increase during an ultra-marathon. An ultra-marathon often leads to a temporary reduction in renal function. Ultra-marathoners often suffer from upper respiratory infections after an ultra-marathon."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5992463/

"A structural change of the heart muscle by an ultra-marathon could be detected by the use of echocardiography. Echocardiography can detect a reduction of the left (Niemela et al., 1984; Krzeminski et al., 2016; Maufrais et al., 2016) as well as the right ventricular (Oxborough et al., 2011; Lord et al., 2015, 2016b; Maufrais et al., 2016; Rothwell et al., 2018) function after an ultra-marathon. The changes in cardiac troponin I during an ultra-marathon are inversely associated with left ventriculare ejection fraction determined with echokardiography (Christensen et al., 2017).

The length of the ultra-marathon is important whether a change in the left and/or right ventricular function occurs. After the 2-day “Lowe Alpine Mountain Marathon,” both a systolic and diastolic dysfunction of the left ventricle could be detected. Humoral markers of myocardial damage were increased and the increase in cardiac troponin was considered to be associated with a minimal myocardial damage (Shave et al., 2002). After a 24-h ultra-marathon, two out of 20 runners showed a slight increase in cardiac troponins and echocardiography showed a decrease in left ventricular ejection fraction in one of the two runners (Passaglia et al., 2013). After an 89-km ultra-marathon, there was a reduced function of the left and right ventricles (Chan-Dewar et al., 2010). In a 4-h run, there was a decrease in the activity of the MIBG (131-J meta-iodo-benzylguanidine) in the myocardium, and the extent of activity decrease correlated with the distance covered during the run (Estorch et al., 1997). In a 160-km ultra-marathon, no correlation between the decrease in left ventricular function and the change in cardiac biomarkers could be demonstrated (Scott et al., 2009). During a 24-h ultra-marathon, the left ventricular function decreased during the last 6 h of the race where the function normalized within a few days after the race (Niemela et al., 1984). Another study showed that echocardiographic changes returned to normal within 1 day after the run (Dávila-Román et al., 1997). In some instances, an ultra-marathon leads to no echocardiographic changes. For runners in the “Western States Endurance Run,” echocardiographic findings were normal (George et al., 2011). Therefore, it is at the moment difficult to conclude that an ultra-marathon leads to substantial heart damage."

Thanks for the reference. It's just hard for me to parse out how bad it is for me to continue running these kinds of distances.

One could easily write a list of scary side effects for being sedentary too... but which is worse? I'm just guessing (hoping) that the benefits of marathon running outweigh the costs.

The choice isn't marathons or nothing. You could run half-marathons.

Parent's last sentence gives me hope it should be OK, at least for the heart.

What I can surely say is that I have never been feeling better and healthier than since I started running long distances at 30.