['Heart surgery with extracorporeal circulation has a marked effect on platelet function and coagulation accounting for abnormal blood loss and allegedly a low incidence of thromboembolic complications. Little is known about platelet function at the time of hospital discharge of routine patients.', 'Blood samples from 91 patients undergoing elective heart surgery were drawn before surgery and prior to discharge. Thirty-seven patients underwent coronary artery surgery and 54 an aortic valve implantation. The mean age of patients was 69+/-9 years. Fifty patients were male and 41 female. Platelet function was evaluated using plasma beta-thromboglobulin quantification in enzyme-linked immunosorbent assay. In addition, flow cytometric analysis of platelet-monocyte conjugates and platelet-neutrophil conjugates was performed.', 'The platelet count before discharge was significantly increased (265+/-86 vs. 212+/-61 x 10(9)/l preoperatively). beta-Thromboglobulin was significantly increased (176+/-127 vs. 79+/-70 ng/ml preoperatively) and flow cytometry proved a significant increase in monocyte-platelet aggregates (8.3+/-5.4% vs. 5.3+/-2.6% preoperatively) indicating platelet activation at the time of hospital discharge. There were no significant differences among the three subgroups coronary surgery, mechanical valve insertion and biological valve insertion.'] Does heart surgery with extracorporeal circulation lead to platelet activation at the time of hospital discharge?