Open heart surgery involving the use of artificial prosthetic materials, and extracorporeal circulation for varying periods, is often performed on patients seriously or acutely ill. Despite excellent surgical procedures, various postoperative complications may detract from perfect primary results. Postoperative myocardial failure and cardiac arrhythmias can be expected while vascular accidents and disorders of various organ systems are less common, but serious, complications. The treatment of these complications requires correct diagnosis without delay, their recognition being particularly difficult during the immediate postoperative period. This review deals with the incidence, diagnosis and therapy of the most important early postoperative complications specific to open heart surgery.