Increased left ventricular mass has been established as a strong risk factor for cardiovascular morbidity and mortality. To evaluate growth of left ventricular mass from childhood into early adulthood and its possible sociodemographic, anthropometric, and hemodynamic moderators, individual growth curves across age of left ventricular mass were created for 687 African American and European American males and females with a maximum of 10 annual assessments (age, 8.2 to 27.5 years). African Americans and males had significantly greater left ventricular mass (P<0.001) than did European Americans and females, respectively. Males also showed a larger rate of change in left ventricle mass than did girls (P<0.001). The ethnicity and gender effects on left ventricular mass only became apparent in early adolescence, and they persisted when controlling for socioeconomic status and anthropometric and hemodynamic variables. Body mass index and height were the strongest anthropometric predictors, and pulse pressure was the strongest hemodynamic predictor of left ventricular mass. Although significant, the contribution of pulse pressure to the prediction of left ventricular mass was small, once body mass index and height were entered into the model. The results of the present study suggest that increased left ventricular mass in boys and African Americans has its origin in late childhood. Apart from these ethnicity and gender effects, individual differences in cardiac growth can mainly be explained by body growth and increases in general adiposity.