Left ventricular shape and function were studied in 12 normal subjects, 18 patients with pressure overloading secondary to isolated aortic stenosis and 20 patients with volume overloading due to aortic regurgitation. End-diastolic volumes were mildly increased in aortic stenosis but greatly increased in aortic regurgitation. Average ejection fractions were normal in aortic stenosis but depressed in aortic regurgitation. Ventricular shape (eccentricity), normal (elongated) in nearly all patients with aortic stenosis, showed in diastole various degrees of abnormal roundness in patients with aortic regurgitation. As ventricular function declined in aortic regurgitation, the ventricles also became more round in systole. After valve surgery, clinical results were generally better in patients with aortic stenosis than in patients with aortic regurgitation. Among the latter, changes in eccentricity and ejection fraction were the best predictors of surgical outcome. It is postulated that chronic volume loading, as exemplified by aortic regurgitation, may induce basic alterations in architecture and fiber alignment of the left ventricular wall. Such changes may exert significant influence on the clinical course of these patients.