A fetus weighing 947 g was autopsied after prenatal echocardiographic diagnosis of a single ventricular heart. At autopsy a single ventricle was present with a pear-shaped scar in the area presumed to represent the right ventricle. A small stoma from the single ventricle connected to the scar and the pulmonary outflow was obstructed. The left coronary artery was occluded and on histologic examination recanalization was seen. A chromatographic peak which closely eluted with the cocaine metabolite, benzoylecognine, was identified in fetal urine. We postulate that coronary spasm following possible cocaine exposure could have produced an infarct which destroyed the right ventricle. It is possible that this fetal pathology may be one mechanism that leads to single ventricle hearts.