We experienced three cases of unusual cardiac hypertrophy of the right ventricle or interventricular septum with severe congestive heart failure in the neonatal period. One patient had congenital heart disease consisting of membranous tricuspid atresia, absent pulmonary valve, patent ductus arteriosus, left single coronary artery and a hypoplastic pouch-like right ventricle. Very marked cardiac hypertrophy was observed in the right ventricle and interventricular septum. Histologically, there was no appreciable disorganization of the cardiac muscle. The etiology of the unusual hypertrophy of cardiac muscle in this patient is uncertain. The other two patients had asymmetrical septal hypertrophy of the left ventricle evidenced by two-dimensional echocardiography. Cardiac catheterization was performed for these two patients. There was no evidence of congenital heart disease; however, one patient had a significant pressure gradient in the outflow tracts of the left and right ventricles. These two patients' faces appeared unusual and they had minor anomalies of their fingers and ears. This unusual cardiac hypertrophy associated with cardiac anomalies and minor anomalies of the face and extremities comprise a specific type of cardiomyopathy in neonates. This should be distinguished from hypertropic cardiomyopathy of older children and adults.