Since it is usually a complication of a more easily recognized disease, acute pericarditis in the absence of an obvious pericardial friction rub or of a striking pulsus paradoxus is frequently overlooked. Despite the fact that a definite electrocardiographic pattern almost pathognomonic of acute pericarditis has been described, the value of this method of dignosis has not been generally recognized. In our limited experience, moreover, several electrocardiograms typical of acute pericarditis have been erroneously attributed to coronary occlusion. In 1929 Scott, Feil and Katz1described transitory elevation of the RT segments in all three leads of the electrocardiogram in a case of hemopericardium and in one of purulent pericarditis. These changes were attributed to cardiac tamponade resulting from increased amounts of pericardial fluid and it was emphasized that this type of electrocardiogram could be differentiated from that of acute myocardial infarction. Since then electrocardiographic changes have been described by