Humans are more similar in transmural Purkinje and cardiac ion channel distributions to dogs than pigs. The Purkinje network in pigs is transmural but confined to the endocardium in dogs. Little is known about intramural activation during long-duration ventricular fibrillation (LDVF) given these differences. We tested the hypothesis that the transmural activation sequence is similar in sinus rhythm (SR) and LDVF in dogs as well as pigs, but different between species.