Sodium nitroprusside (SNP) is known to inhibit platelet aggregation and has been implicated in postoperative hemorrhagic complications. Because it is a useful agent for treating postoperative hypertension and low cardiac output in the cardiac surgical patient, the authors retrospectively reviewed the course of 53 patients undergoing open heart procedures on cardiopulmonary bypass.Twenty-three patients received SNP and 30 did not. There were no differences in baseline hematological or clotting profiles, liver functions, bypass or cross-clamp times or heparin/protamine requirements between the two groups.Analysis revealed no significant differences between the groups in blood product requirements, actual mediastinal drainage, or postoperative measurements of routine clotting parameters.Although biochemical inhibition of platelet aggregation can be demonstrated, the use of SNP in the cardiac surgical patient has no apparent clinical effects which should detract from its utility in treating hypertension or low cardiac output.