The true incidence of congenital pericardial defects is unknown, but it is more common than generally supposed. Because of the variance of chest X-rays, ECG and symptoms according to the degree of the defect, it is still not easy to diagnose a pericardial defect. Recently, we experienced four patients with congenital pericardial defects. Three cases were absence of the left pericardium and one was an absence of the right. In these patients, the view with echocardiography was characteristically altered by posture changes. All three patients with left-sided defect showed an enlarged right ventricular cavity, paradoxycal motion of the interventricular septum and hyperkinetic motion of the posterior wall in the left lateral decubitus position. These findings were not present in the right decubitus position. On the other hand, in a case with a right-sided defect, the view was almost normal in the left decubitus position. In the right decubitus position, the right ventricular cavity enlarged and the interventricular septum moved hyperkineticaly. These alterations of echocardiographic findings by posture changes were specific to the side of the pericardial defect, and were caused by a change in cardiac restraint. Therefore, an echocardiogram recorded with posture changes is useful in the diagnosis of congenital pericardial defects.