Left ventricular rotation about the longitudinal axis of the heart has been qualitatively described but difficult to quantitate. Cross-sectional echocardiography offers a simple, noninvasive method for determining both the presence and degree of left ventricular rotation. In this study we examined normals and patients with various forms of heart disease for angular displacement of the papillary muscles during the cardiac cycle. Assuming that the papillary muscles represent fixed internal reference points, angular displacement of these points represents left ventricular rotation about the longitudinal axis. Short-axis, cross-sectional echocardiograms were recorded in 100 patients 34 normals, 16 patients with secundum atrial septal defect and 50 patients with various forms of valvular, congenital and ischemic heart disease. Angular displacement of the papillary muscles was determined by measuring the angle subtended between a line drawn parallel to the chest wall and a second line drawn through the tips of the papillary muscles. The degree of angular displacement of the papillary muscles was then derived by subtracting the diastolic angle from the systolic angle. This value was interpreted to represent the degree of left ventricular rotation about the longitudinal axis during the cardiac cycle. The normal group had a minimal degree of counterclockwise left ventricular rotation (mean 3.00; range 0-6%deg;). Exaggerated counterclockwise left ventricular rotation was noted in patients with secundum atrial septal defect (mean 17.20; range 9-29%deg;; p < 0.001). Eight of these patients were studied after surgical closure of the defect, and the pattern of left ventricular rotation was not significantly different from that in normals (mean 3.3%deg;; range 2-5%deg;). The third group of patients, who had various forms of heart disease, including right ventricular volume and pressure overload, had minimal left ventricular rotation (mean 3.20; range 0-7%deg;). e conclude that minimal counterclockwise left ventricular rotation occurs in normals and patients with heart disease. Exaggerated left ventricular rotation is characteristically observed in patients with secundum atrial septal defect, and is abolished after surgical closure of the defect.