Auriculoventricular rhythm, a condition in which the A-V node assumes rhythmicity independent of the sinus node, is due to one of two causes; depressed irritability of the sinus node or enhanced irritability of the A-V node. Experimentally both types have been produced, the former by tying off (Engelmann1), injuring (Hering2), or cooling (Ganter and Zahn3) the sinus node, the latter by stimulating the A-V node either directly (Lohmann4) or through the left accelerator (Hering;5 Rothberger and Winterberg6). Meek and Eyster7 reviewed and extended the experimental work. By means of electrodes connected with a string galvanometer and applied direct to the heart they obtained evidence that in A-V rhythm the electrical activity originates in the A-V node. Clinically, both types of the A-V rhythm have been observed, the type in which the irritability of the sinus node is depressed, characterized by a slow rhythm, and the type in which the irritability