The cardiac hemodynamic effects of patent Brescia Cimino fistulas were assessed using non-invasive techniques in 10 pediatric patients who had undergone successful renal cadaveric transplantation. All had hemoglobin levels above 11 g/dl and had serum creatinine values of less than 1.5 mg/dl. Studies were done prior to and after temporary fistula occlusion to assess the effect of fistula patency on parameters of cardiac function. Values obtained prior to fistula occlusion were compared to those obtained in a normal control population. It was noted that though fistula patency did significantly alter cardiac function, changes were such that fistula patency could be safely maintained. It was also noted that the difference in cardiac index prior to and after occlusion provided a good assessment of fistula flow.