The evaluation of the growth of the cardiac transplant in children was studied in four young children and three infants by echocardiography after orthotopic transplantation. These children were all under 13 years of age at the time of transplantation and have been followed up for more than two years. The age of the recipients ranged from 2 days to 12.8 years (average 10.7 years) and that of the donors from 7 days to 27 years (average 6.7 years). All patients received triple immunosuppressor therapy. The follow-up was 29 to 48 months (average 39.7 months) in the infants and 28 to 71 months (average 50.25 months) in the children. In the 7 patients the global follow-up period ranged from 28 to 71 months (average 45.8 months). No episodes of acute rejection or hypertension were observed during the study period. The echocardiographic parameters studied were the left ventricular end diastolic dimension, left ventricular end systolic dimension, left ventricular mass, left ventricular mass index. The date was gathered prospectively during the study at monthly intervals after the 3rd postoperative month. The donor/recipient weight ratio varied from 0.83 to 5 (average 1.89). The growth of the recipients was normal in 5 out of 7 cases and moderately retarded in 2 cases. The left ventricular end diastolic dimension, left ventricular end systolic dimension and left ventricular mass increased linearly with the body surface area of all patients. The growth was faster in the infant patients.(ABSTRACT TRUNCATED AT 250 WORDS)