In the immediate postoperative period, echocardiography was used to study left ventricular function in 69 children after correction of various congenital cardiac malformations. Left ventricular contractility indices and systolic time intervals measured from aortic cusp echoes were repeatedly obtained during the fist postoperative week. The degree of impairment of left ventricular function was assessed for different diagnostic groups and are tabulated. Decrease in left ventricular function was strongly correlated to operating time, cardiac bypass time, and aortic clamping time, the most important factor being cardiac bypass time. Left ventricular ejection time (LVET) was the most useful parameter of cardiac function in the immediate postoperative period and was of prognostic value in 5 patients who died early in that period. Abnormal septal movement was seen in most patients, but usually normalized within 2 wk. After extensive operations, changes in the movement pattern of the aortic leaflets were also seen. Although pericardial effusion was commonly found during the postoperative period, it did not indicate postcardiotomy syndrome and disappeared spontaneous within 2 mth.