Sinus node dysfunction is common after orthotopic heart transplantation.Electrophysiologic studies have documented a high incidence [46% to 50%] of impaired sinus node automaticity and sinoatrial conduction in the early posttransplantation period. Sinus node dysfunction persists in over 20 % of patients and leads to prolonged bradyarrythmias, including sinus or nodal bradycardia and sinus arrest.The purpose of this paper was to observe sinus node dysfunction after orthotopic heart transplantation. Ten cardiac recipient dogs were monitored continuously after orthotopic transplantations between unrelated adult mongrel dogs. Crystalloid cardioplegic solution [Choongwoi Cardioplegia