A left ventricular assist device (VAD) with a smooth surface of segmented polyurethane was implanted in five goats for 10-55 days, and plasma levels of fibrinogen (Fg), prekallikrein (PK), fibrinogen, fibrin degradation products (FDP), antithrombin III (AT III), prothrombin time (PT), partial thromboplastin time (PTT), platelet (Pl) count, and platelet aggregation (PlAg) induced by adenosine diphosphate were measured during the experiment. Heparin was administered during surgery and no systemic antithrombotic therapy was given thereafter. Before the third postoperative day (POD), plasma levels of Fg and PK were at their lowest, and increased afterward. Between the second and fifth POD PT and PTT increased to 130-160%, and returned to normal gradually. Plasma FDP appeared on the second POD and reached peak values of 10-40 micrograms/ml on the sixth POD. Platelet and AT III levels showed no uniform tendency, but the rate of PlAg decreased to levels of 6-77% before the fifth POD and remained low at approximately 80%, influenced by the pumping even after the 25th POD. In summary, VADs themselves activated coagulation and induced consumption coagulopathy to some degree. However, most of the parameters returned to normal within 2 weeks.