Frame by frame analysis of left ventriculograms has been performed in 10 normal subjects and 40 patients with heart disease. Left ventricular shape index was derived as 4 pi (cavity area)/(perimeter)2, which has a maximum value of 1 when the outline is circular. In normal subjects systole was always associated with progressive reduction in shape index, indicating that the cavity projection had become less circular. This change was smaller in patients with low ejection fraction and also when inferior or anterior hypokinesia was present, even though ejection fraction was normal. During early diastole shape index rose rapidly due to an increase in minor diameter occurring throughout the period of rapid filling. In some cases this preceded any change in long axis, which was due to upward movement of the aortic root as well as outward movement of the apex. These results have functional implications, suggesting in particular that wall movement during filling may be non-uniform and that assumptions about cavity shape used in the derivation of wall properties from estimates of ventricular volume may require modification.