Athletic training induces a morphologic adaptation of the heart, by increasing left ventricular cavity size and wall thickness. Wall thickening usually ranges up to 12 mm, but in 2% of athletes it may be more marked (13-16 mm). Athletes with the most substantial wall thickening are rowers, canoeists, and cyclists, competitive at elite levels for a substantial period of time. Therefore, physiologic left ventricular hypertrophy probably does not exceed 16 mm in thickness and is usually present in the ventricular septum, associated with an enlarged cavity size. Additional features of the physiologic left ventricular hypertrophy are the regression of wall thickening into normal limits (less than 13 mm) after a period of deconditioning and the consistent normality of the Doppler diastolic filling pattern.