In this presentation our experience of the correction of large ventricular septal defects (VSD) under deep hypothermia (DH) and reduced flow rates in infants is reported. Sixty patients with VSD and pulmonary hypertension were operated. The age of the patients varied from 1.5 to 12 months and body weight from 3.0 to 8.7 kg. Deep hypothermia was achieved by cooling the patient using a heart-lung machine after aortic and right atrial cannulation. At a rectal temperature of 18 degrees C, pump flow was reduced to 0.28 l . min-1 . m-2 and cardiotomy was performed. Venous blood from the right atrium was aspirated with a single coronary sucker. The aorta was not clamped. After completion of the intracardiac repair, pump flow was increased and the patient was rewarmed to a rectal temperature of 36 degrees C. In all cases cardiac rhythm was restored spontaneously during rewarming. In every patients, the VSD was closed with a xenopericardial patch (in 42 patients from a right atrial approach and in 18 patients through the ventriculotomy). In 5 patients a patent ductus was also ligated and in 37 patients an atrial septal defect was sutured. The hospital mortality was 5% (3 patients). In the remaining 57 patients the cardiac index during the first 48 hours after operation was 2.5-4.2 l . min-1 . m-2. Patients were extubated between 18 and 44 hours after the operation. Deep hypothermia with reduced flow rates during intracardiac repair provides excellent myocardial protection and exposition in infants with VSD.