Electrocardiographic (ECG) changes are described after heart transplantation in almost 75% patients. During the early postoperative period the usual finding are conduction disorders which in 3-5% call for implantation of a pacemaker. The most frequent persisting disorder is bundle branch block which is of clinical importance only when it has a progressive character. The incidence of postoperative atrial fibrillation or flutter is lower as compared with other cardiosurgical operations and their sudden development may be associated with acute rejection. Ventricular arrhythmias develop as a rule as a complication of advanced coronary disease of the graft and are frequently the cause of sudden death. Before the introduction of cyclosporin A a relatively reliable sign of acute rejection was a reduction of the QRS complex voltage. During contemporary treatment ECG changes develop only in severe forms of rejection, incipient changes can be recorded only by an intracardial electrogram.