Bigeminal pulsation in atrioventricular rhythm is extremely rare. In 1915, the electrocardiograms of an unique case seen at the Massachusetts General Hospital were published.1 During the past year, a second case showing the same condition has been examined, also at the Massachusetts General Hospital. No other cases have been reported in the literature, so far as I am aware.2 Atrioventricular rhythm, once called "nodal rhythm," is that cardiac rhythm arising from the atrioventricular node (of Tawara) which lies in the connective tissue below the endocardium of the right auricle just above the septal edge of the tricuspid valve ring. Impulses arising in this node travel in both directions, upward to produce an upside-down contraction of the auricles, and downward to produce ventricular systole. If the a-v node stimulates the ventricles alone while the sino-auricular node (the normal "pacemaker" of the heart) stimulates the auricles, auriculo-ventricular dissociation occurs either of the