Vulnerability to fibrillation and the ventricular-excitability curve.

P REVIOUS reports have given a description of the cyclic changes in excitability of both auricle and ventricle of the dog’s heart (I, 2). It was found that the dog’s auricle is ‘vulnerable’ to fibrillation throughout the major dip area of the excitability-recovery curve (3). A study of ventricular vulnerability has now been made. Cats and turtles were used almost exclusively in this investigation because their smaller hearts could be defibrillated more easily than the ventricle of the dog. The secondary purpose of this study was to determine whether or not the phenomena of the recovery of excitability are similar in the hearts of different vertebrates.