Simultaneous measurement of atrial and ventricular pacemaker activity.

The isolated perfused rat heart with surgically-induced heart block was used to determine the effect of drugs on the activity of the atrial and ventricular pacemaker simultaneously. Complete atrio-ventricular dissociation was produced by tying a ligature around the Bundle of His under direct vision. Pacemaker rates remained stable for at least 2 hours. Perfusion of the hearts with quinidine produced a decrease in the rate of both the atrial and ventricular pacemaker. The ventricular pacemaker was more susceptible to the depressant action of quinidine than the atrial pacemaker.