How Runners’ Hearts are Different

An endurance athlete’s heart can be up to 50 percent bigger than a nonathlete’s heart.

The atria, the upper two “filling chambers” where blood arrives in the heart, are enlarged, as are the ventricles, the two lower chambers that pump blood to the rest of the body.

The vessels that supply blood to muscles of the heart are able to expand more to allow more bloodflow during exercise even when there are some cholesterol deposits. This ability to dilate makes it easier for blood to get around any partial blockages.

The secondary network of vessels that distribute blood to muscles of the heart may be two to three times bigger than normal.

A: Cross-section of a coronary artery shows the plaque accumulation of atherosclerosis: blobs of cholesterol (yellow) with dots of calcium (blue).

B: In patients taking statins, plaques tend to have less cholesterol but more calcium, which hardens into dense bands. This leads to high coronary artery calcium scores, but dense plaques may be less likely to rupture and cause a heart attack. Emerging evidence suggests that plaques in runners, too, may be denser and more stable.