Cardiac tumours and anatomical malformations of the heart may produce similar clinical signs and symptoms. The coexistence of these two abnormalities complicates diagnosis and probably adversely affects prognosis. We present a review of four cases of this rare combination. In the first case, Ebstein's malformation was present in a child with tuberous sclerosis and cardiac rhabdomyomata. Right ventricular rhabdomyomata were associated with a hypoplastic tricuspid valve in the second case. In the third case, cardiac myxomas were detected in a child with a double-chambered right ventricle. The fourth case was a child with a fibroma of the right ventricle with pulmonary atresia. We propose that, in some circumstances, a space-occupying lesion may be associated with, or possibly induce, a malformation within the developing heart.