M-mode echocardiograms were obtained from 40 sedentary college women, 8 sprinters, 6 distance runners, 10 swimmers, 9 basketball players, 8 dancers, and 10 sedentary men (ages 19 to 31 yr). Treadmill stress tests were performed by all groups except the basketball players. The aerobic capacities of the athletes were 30 to 48% greater (P less than 0.05) than the sedentary subjects. The athletes exhibited trends toward higher than average left ventricular (LV) end-diastolic dimensions (7 to 25%), LV end-diastolic volumes (12 to 53%), stroke volume (13 to 52%), LV mass (11 to 42%), and left atrial dimensions (6 to 31%) when data were standardized for body surface area. A correlation (r = 0.323, P less than 0.05) was noted between LV mass index and maximal oxygen uptake when data were pooled. Ten sedentary women and ten age-matched sedentary men were endurance-conditioned by 10 wk of running. Both sexes increased maximal oxygen uptake approximately 20% (P less than 0.05) and exhibited similar changes in LV wall thickness, end-diastolic dimension, end-diastolic volume, and mass. These changes regressed within 10 wk after the termination of conditioning. This study suggests that women athletes exhibit cardiac morphologic features which resemble that reported for their male counterparts and that the cardiac response of sedentary men and women to modest levels of endurance conditioning is similar.