Emergency cardiac surgery has been performed on 18 cases of acute cardiac tamponade whose etiologies were as follows: 11 cases of metastatic carcinoma, four cases of idiopathic pericarditis and three with other causes. In most cases, the chief complaint was dyspnea. In many cases, the cardiac silhouette of frontal chest X-ray films showed the shape of a water-filled ice-bag placed on a table. The electrocardiogram showed a low voltage and a flat T-wave in approximately half of the patients. In cases of an echo-free space 1 cm or larger on the M-mode echocardiogram, the average amount of pericardial fluid drained was 850 ml and in those in which the space was less than 1 cm, the average drained was 557 ml. The CT values were 9-40 for patients with malignant pericardial effusion and 20-22 for cases of idiopathic pericarditis. In general, pericardiocentesis was performed in almost all the patients with acute tamponade, but if the drainage was inadequate, the subxiphoid pericardial window procedure was performed under local anesthesia. Surgical invasion in this technique was minimal and the operative results proved effective. For the operation, we resected a 2 X 2 cm pericardial segment. Since two of the patients with malignant pericardial effusion developed postoperative reaccumulation, resection of a 4 X 4 cm segment in the future has been contemplated.