It is common knowledge that your muscles become stronger and thicker if you exercise them frequently. The same is true of the heart muscle. Athletic heart (athlete’s heart) is hypertrophy (thickening of the walls) due to the regular physical training. Well trained athletes have a slow heart rate and sometimes lower grades of atrioventricular blocks (block in the conduction of electrical signals from the upper chambers of the heart to the lower chambers) as part of the athletic heart syndrome. Lower resting heart rates in trained athletes prevents undue increase in heart rates with exercise. The opposite is seen a physically deconditioned individual, who has a rapid increase in heart rate even with low grades of exercise.
It is important to differentiate between athletic heart syndrome from hypertrophic cardiomyopathy (an inherited disorder of the heart muscle characterized by gross and often asymmetric thickening of the heart muscles) as the latter condition can cause sudden death during sports. The ideal method of differentiating this hypertrophy due to training from other causes is by deconditioning. That is to stop athletic training for a few weeks and observe whether the hypertrophy regresses. If it regresses, it is true athletic heart. If not, other causes like hypertrophic cardiomyopathy have to be thought of. Athletic heart is a physiological (natural) response to exercise training and is not considered as a disease state. It is an adaptation of the heart to constantly increased work load imposed by exercise training and allows the heart to deliver more blood to the exercising muscles with an elevated oxygen demand.