Heart transplantation is the treatment of choice for those with end-stage heart failure. However, despite improvements in immunosuppressive treatment, patients are at significant risk of allograft rejection, especially early after transplantation. Any changes in patient's heart condition including reduced left ventricular ejection fraction, arrhythmia and any types of blocks need attention. Herein we report on a 29-year-old man who underwent heart transplantation 5 years before due to dilated cardiomyopathy. He was on immunosuppressive therapy and was good until one week before his admission, when he felt palpitation. Electrocardiography during palpitation showed a second-degree AV-block with heart rate of 60 beats/min. Echocardiography showed good left ventricular systolic function with no regional wall motion abnormality. The patient referred for coronary angiography and endomyocardial biopsy. The angiography was normal. The biopsy showed rejection compatible with ISHLT grade 2R. After treating the patient with 1.5 g methylprednisolone, the symptoms relieved and the block resolved. Bradycardia and second-degree AV-block late after heart transplantation could be a sign of cardiac allograft rejection and need more evaluation, especially endomyocardial biopsy.