Primary cardiac tumours are rarely found and have an incidence of 0.3% in all open-heart surgeries. Among those, approximately 70% are myxomas, most of them in the left atrium. The reported incidence of cardiac tumours in autopsy series is 0.001-0.28%. Right atrial myxomas are uncommon, but when present they often originate from the interatrial septum, and conduction disturbances are rarely noted as an accompanying feature in this condition. We report the case of an 18-year-old boy with a myxoma in both left and right atrium associated with atrioventricular dissociation.