Background. Plsma pheresis and reinfusion of platelet-rich plasma has not been shown to reduce blood loss in cardiac patients. Recently, freshly prepared autologous platelet concentrates (PC) can be made from patient’s blood and has a higher concentration than conventional platelet rich plasma. In this study, the effects of autologous PC reinfusion were examined after open heart surgery in patients with congenital heart disease.Methods. Eight patients with noncyanotic congenital heart disease, who underwent open heart surgery and reinfusion of autologous PC, were classified as the PC group. Eight other patients with noncyanotic congenital heart disease, who underwent only open heart surgery, were defined as the control group. Ages ranged from 2 to 24 years and were not significantly different between the two groups (9.3 ± 5.1 years in the PC group and 12.6 ± 7.9 years in the control group, p = 0.33). In the PC group, blood was collected from the femoral vein through a 6F catheter introducer; 9 to 20 U (13.0 ± 5.4 U, 0.42 ± 0.22 U/kg) of autologous PC were prepared and were reinfused after protamine administration. The time course of platelet counts was examined until postoperative day 7. Aggregation responses to adenosine diphosphate; (4 μmol/L and 8 μmol/L), collagen (1 μmol/L and 5 μmol/L), and epinephrine (5 μmol/L and 10 μmol/L) were evaluated after induction of anesthesia (individual references), after protamine administration, at the end of the operation; these responses were shown as recovery ratios.Results. Blood loss during surgery in the PC group was significantly less than in the control group (4.8 ± 3.0 mL/kg versus 7.8 ± 1.7 mL/kg, p = 0.044). Similarly blood loss on postoperative day 1 in the PC group was significantly less than in the control group (3.6 ± 1.2 mL/kg versus 7.2 ± 3.1 mL/kg, p = 0.013). The platelet counts in the PC group were larger than those in the control group until postoperative day 5, after reinfusion of prepared autologous PC. The recovery ratios of the aggregation responses to adenosine diphosphate, collagen, and epinephrine after protamine administration were not significantly different between the two groups. However, recovery in the PC group after reinfusion of the prepared autologous PC was greater than in the control group.Conclusions. Reinfusion of the freshly prepared autologous PC was followed by good aggregation responses and low blood loss in patients with noncyanotic congenital heart disease after open heart surgery. This procedure may be useful in pediatric open heart surgery without blood transfusion or with little administration of homologous blood products.