Abstract Withdrawal of autologous plasma offers the possibility of improving patients' hemostasis and of reducing homologous blood consumption in cardiac surgery. The influence of acute, preoperatively performed plasmapheresis (APP) on platelet function was investigated in elective aortocoronary bypass patients subjected to APP producing either platelet-poor plasma (PPP; group 1; n = 12) or platelet-rich plasma (PRP; group 2; n = 12). APP-treated patients were randomly compared to patients without APP (control group; n = 12). Platelet aggregation induced by ADP (concentration 0.25, 0.5, 1.0, and 2.0 μmol/L), collagen (4 μL/mL), and epinephrine (25 μmol/L) was determined by the turbidometric method before and after APP, as well as before and after cardiopulmonary bypass (CPB) until the morning of the 1st postoperative day. APP had no negative effects on the patients' aggregation parameters (maximum aggregation and maximum gradient of aggregation). The platelet counts in the withdrawn plasma were 25 ± 10 × 10 9/L (PPP-group) and 250 ± 30 × 10 9/L (PRP-group). Platelet counts were highest in the PRP-group at the end of the operation (after retransfusion of autologous plasma). After CPB, maximum aggregation and maximum gradient of aggregation were reduced in all groups (ranging from −6% to −25% from baseline values). Retransfusion of autologous plasma improved platelet aggregability significantly only in the PRP-group. By the first postoperative day, maximum aggregation and maximum gradient of aggregation recovered in all groups (including the control group) or even exceeded baseline values (ranging from +8% to +42% from baseline values). Total postoperative blood loss was 600 ± 150 mL in the PRP-patients and 950 ± 250 mL in the control group ( P = 0.07). PRP-treated patients did not receive homologous blood, whereas 3 control patients received a total of 5 units of packed red cells ( P < 0.05). The results of this study demonstrate that APP-withdrawn PRP did not only increase platelet count effectively, but also improved the platelet's aggregability in the postbypass period. Thus, preoperatively performed plasmapheresis may help to optimize patients' hemostasis and reduce homologous blood usage.