Long-term observation of atrial and ventricular rates in the unanesthetized dog with complete atrioventricular block

The evolution of atrial and ventricular rates was studied in unanesthetized dogs with complete A-V block over a three-year period. During the first 40 days after A-V block, atrial rate far exceeded the sinus rate recorded before surgery, but had fallen progressively back to this level by the 41st day, and remained there until the end of the three-year period. Ventricular rate had settled down to a plateau by the 31st day. These findings explain certain differences among previously reported results, and have led us to use such animals for drug studies only after the beginning of the third month after creation of the complete A-V block.