Cardiomegaly

One side of the heart may become disproportionately larger than the other depending on training variables, a condition called hypertrophy. Endurance training can cause cardiomegaly, an overall enlargement of the heart. One-third of marathoners experience dilated ventricles, where the ventricles on one side become abnormally enlarged. Endurance exercise is associated with heart muscle damage and cardiac fibrosis that can lead to serious cardiac complications.