Miliary neonatal hemangiomatosis is a rare, life-threatening condition associated with cutaneous and multiorgan involvement. We report two infants with this condition who had fulminant cardiac failure and cardiac septal hypertrophy. The first was a 5-day-old boy who presented with increasing numbers of cutaneous hemangiomata associated with worsening cardiac failure. Magnetic resonance imaging (MRI) showed extensive hepatic hemangioma. Despite treatment with systemic corticosteroids and subcutaneous interferon alfa-2b his disease progressed. Hepatic artery embolization was unsuccessful. The infant died of congestive cardiac failure at 6 weeks of age. Postmortem examination showed a massively enlarged cardiac interventricular septum and biventricular hypertrophy. The second patient was a 1-week-old girl who also had cutaneous hemangioma and cardiac decompensation. MRI showed extensive intrahepatic involvement. She was treated early with corticosteroids and interferon alpha, which resulted in involution of the cutaneous and hepatic lesions. Cardiac septal hypertrophy did not persist at late follow-up, and the association of miliary neonatal hemangiomatosis and cardiac septal hypertrophy has not yet been established.