From left to right are a normal heart, an athlete’s heart, and an athlete’s heart with hypertrophic cardiomyopathy disease (HCM). Cellular changes are shown in the insets. Both of the athletes’ hearts have enlarged walls compared to the normal heart. At centre this is a normal physiological adaptation to exercise. However, the enlargement at right is abnormal, with disrupted alignment of the heart cells, which impairs the functioning of the heart. HCM is often asymptomatic, but can cause sudden cardiac death.