It is generally recognized that electrocardiography adds little to the clinical diagnosis of pulsus alternans. While the electrocardiogram may show evidence of slight or widespread coronary and myocardial involvement, paradoxically it rarely demonstrates alternation of the ventricular complexes as one, a priori, might expect. The two cases of electrical alternans without pulsus alternans we are about to describe—the first to be reported in this country—are in sharp contrast to the usual type of alternans, which is confined to the pulse, heart sounds or apex beat, without evidence of electrocardiographic alternation. The electrocardiographic finding of electrical alternans, judging from the literature and our own experience, is an exceedingly rare phenomenon. Our first case, observed in March 1933, constitutes the only one we have seen in a series of approximately 10,000 electrocardiograms covering a period of about thirteen years. However, since the appearance of the first case, three additional cases of electrical