Cerebral ultrasonography was performed in 66 infants before and after open heart surgery in order to study the incidence of cerebral complications. The underlying cardiac malformations were ventricular septal defect (n = 28), transposition of the great arteries (n = 11), tetralogy of Fallot (n = 8), complete atrioventricular septal defect (n = 5), total anomalous pulmonary venous drainage (n = 3), truncus arteriosus communis (n = 2), and complex cardiac malformations (n = 9). In 60 of the 66 infants ultrasonography of the brain preoperatively was normal, 3 had minor structural abnormalities, and 3 had ventriculomegaly of various degrees. Postoperatively, 46 infants had a normal brain ultrasound scan; 6 had slight structural abnormalities; and 5 had slight symmetric or asymmetric widening of the ventricles. Five infants showed severe ventriculomegaly with cerebral atrophy, and in 4 patients there was intracerebral hemorrhage, associated in 2 cases with severe ventriculomegaly. On repeat examinations it was found that up to 4 weeks after the operation an initially normal cerebral ultrasound scan could convert to a pathologic one. Most of those children who showed significant deterioration on the cerebral ultrasound scan suffered from complex cardiac malformations or had severe problems during the postoperative period.