A 2 1/2 year old boy collapsed at home and was taken immediately to the local hospital in cardiorespiratory arrest where attempted resuscitation was unsuccessful. At autopsy, massive cardiomegaly was found associated with a large membranous ventricular septal defect. There was also an early acute bronchopneumonia. Although growth parameters indicated failure to thrive, no specific health problems had been noted by the family apart from an apparent mild 'upper respiratory infection' prior to death. While the occurrence of sudden and unexpected death in cases of undiagnosed isolated ventricular septal defect has not been emphasized in the literature, this case demonstrates that sudden death may be a problem in early childhood. This is particularly so in cases of untreated large defects with cardiomegaly when additional stresses such as acute infection occur.