In brief: Echocardiographic studies permit direct, accurate measurements of the ventricular wall thickness and cavity diameter. The authors review several of these studies, which show that elite athletes' left ventricles are larger than those of sedentary persons. Left ventricular wall thickness is greater in athletes excelling in sports involving static exercise, whereas those in endurance sports have larger ventricular cavities. These differences in cardiac dimensions may be the result of genetic makeup, prolonged and strenuous training, or a combination of both. Studies of short-term training showed only minor or no changes in left ventricular morphology, although significant improvements in performance and aerobic capacity were reported.