In a group of 2811 chest casualties of the Korean conflict treated at Tokyo Army Hospital from August, 1950, to March, 1953, 117 had injuries to heart and mediastinum. This is an incidence of 4.2%. The small number is due, no doubt, to the high initial mortality resulting from such wounds. HEART AND PERICARDIUM Injuries to the heart and pericardium are considered in one group, since both are so often damaged at the same time. Approximately 90% of such injuries were caused by penetrating injuries with the retention of foreign bodies; 10% were due to perforating injuries. Forty-two patients developed pericardial effusions which were usually due to the presence of small metallic foreign bodies within the pericardium. The effusion developed any time from shortly after injury to six weeks later. The patient experienced severe precardial pain, a rise in temperature, tachycardia, and shortness of breath. Upon physical examination, the heart