Low left ventricular ejection fraction (LVEF), a measure of global systolic left ventricular dysfunction, is associated with an increased risk of recurrent coronary events or death in persons with cardiac disease. There are few data on the distribution of resting LVEF and component volumes in healthy young adults or on any associaton of LVEF with coronary risk factors. LVEF and left ventricular end-diastolic and end-systolic volumes (LVEDV and LVESV, respectively) were measured by two-dimensional echocardiography in 1782 men and women 23 to 35 years old without self-reported heart disease (other than mitral valve prolapse, n = 53) who were participants in the multicenter Coronary ARtery Risk Development in Young Adults study. Factors analyzed as potential contributors to LVEF, LVEDV, and LVESV included age, gender, race, blood pressure, alcohol use, current smoking, family history of myocardial infarction, total and high-density lipoprotein cholesterol concentrations, obesity, reported physical activity, and fitness as assessed by treadmill exercise testing. LVEF was lower in men (mean 62.6%, SD 5.7%) than in women (mean 63.9%, SD 5.7%), (p < 0.01) but did not differ significantly between black and white subjects. Ninety percent of subjects had an LVEF between 53% and 71%. LVEDV and LVESV were >25% greater in men than in women. From multivariate analysis, male gender, history of hypertension, and current smoking were each positively and independently associated with an approximately 1% lower LVEF. Body surface area, a family history of premature myocardial infarction, and treadmill workload 150 time were positively related, whereas total skinfold thickness was negatively related to LVEDV and LVESV. In addition, systolic blood pressure was positively related and diastolic blood pressure and total cholesterol concentration negatively refated to LVEDV, whereas treadmill performance measured in metabolic equivalents (METS) and current smoking were positively related and age negatively related to LVESV. These results suggest that LVEF in healthy young adults is maintained over a limited range and that is variability not substantially associated with coronary risk factors. Determination of whether differences in LVEF, LVESV, and LVEDV in young adults influence future cardiovascular risk and whether obesity and other factors express any effect on risk through differences in LVESV and LVEDV will require longitudinal follow-up studies.