Even if you’re super fit, if you have hidden heart artery disease, doing something really intense — like a marathon — can suddenly trigger a heart attack or cardiac arrest.

The presence of increased coronary artery plaque in high-volume endurance athletes is not associated with a higher incidence of clinical cardiovascular events such as myocardial infarction or cardiac death.

Even though super-fit people have more calcium in their heart arteries, they still live longer and have fewer heart attacks — their fitness seems to protect them from the danger of the plaque.

Doing very hard exercise — like sprinting or intense cycling — is linked to more calcium buildup and plaque in the heart arteries, even if the total amount of exercise is the same as someone who exercises less intensely.

High-volume, high-intensity endurance exercise increases coronary artery plaque burden without increasing all-cause or cardiovascular mortality risk in otherwise healthy individuals.

Men who have trained for decades as elite endurance athletes, like cyclists or marathoners, tend to have more fatty deposits in their heart arteries than healthy men who exercise moderately—even when both groups are fit and have normal cholesterol and blood pressure.