BACKGROUND : The authors previously observed that some high-performance athletes, irrespective of type of sport, can show echocardiographically determined low left ventricular ejection fractions (LVEF; <52%) together with normal heart rates and nondilated left ventricular (LV) cavities under resting conditions. The aim of this study was to determine if this phenomenon is associated with dyssynchronous motion of the interventricular septum relative to the lateral LV wall. METHODS : Results of M-mode and two-dimensional echocardiography and pulsed-wave, pulsed-wave tissue, and color tissue Doppler were compared in 70 athletes (mean age, 20 ± 7 years; 77% men) with low LVEFs (<52%) participating in a wide variety of sports and a control group of 564 athletes (mean age, 22 ± 7 years; 61% men) with normal LVEFs (≥52%). RESULTS : No between-group differences were found in cardiac dimensions or QRS duration (indicating no electrical dyssynchrony in the low-LVEF group compared with the normal-LVEF group), but analysis of mechanical interventricular and intraventricular dyssynchrony showed that time intervals between QRS onset and the different systolic waves were all lengthened in the low-LVEF group (P < .05 for all). Values of interventricular mechanical delay were higher in the low-LVEF group (P = .012), though they did not reach pathologic limits. Peak aerobic performance was independent of LVEF. The results did not change materially when analyzing data separately by sex or sport. CONCLUSIONS : Some young highly trained athletes might show depressed LVEF (<52%) with a nondilated LV cavities in the early phase of cardiac adaptations, which seems to be linked to longer LV contraction times, with the right ventricle unaffected. These echocardiographic findings, although not highly prevalent, could be considered another characteristic of the cardiac adaptations to the demands of elite sports with no detriment in performance.