Cardiac findings in adult endurance athletes are well characterized, but data regarding the "athlete's heart" in children are limited. This study evaluated cardiovascular features of 10 male prepubertal distance runners ages 11-13 years compared to 18 physically active but untrained boys. Mean VO2max values on treadmill testing for the two groups were 61.2 (3.2) and 51.1 (4.3) ml.kg-1.min-1, respectively. No significant differences in the frequency of carotid bruits, cervical venous hums, heart murmurs, or third and fourth heart sounds were observed between the groups. Mean resting heart rate was 71 (9) bpm for the runners and 73 (8) for the controls (p > 0.05). No significant differences were seen in EKG intervals, axes, or precordial voltages between runners and controls, and echocardiographic chamber sizes, wall thicknesses, and mass indexed to body surface area were also similar (p > 0.05). This study failed to identify clinical features of the "athlete's heart" in competitive child endurance runners compared to non-trained subjects.