AbstractM‐scanning was found useful in eight patients in whom the diagnosis of pericardial effusion was negative or equivocal with conventional echocardiography. With the patient in the semi‐recumbent position, the records were obtained while the ultrasound beam was sector scanned base toward the cardiac apex. With this technique, a separation of the posterior pericardium epicardium by a divergent echo‐free space was noted when pericardial effusion was present. The divergent nature of the echo‐free space was due to accumulation of pericardial fluid toward the cardiac apex. The shift of pericardial fluid toward the cardiac apex was further demonstrated by elevation of the patient supine to the semi‐recumbent position. The latter position enhances the sensitivity of M‐scanning in the detection of pericardi