This article describes two patients with artificial heart valves who suffered thromboembolytic complications during circulatory assistance using a Biomedicus centrifugal pump. The first case involved a 25-year-old man who presented acute blockage of a mechanical aortic valve. Emergency surgery was performed to replace this valve with a bioprosthesis. Postoperatively the patient developed severe left heart insufficiency and a Biomedicus centrifugal pump was placed between the left atrium and the ascending aorta. After 3 days of total left ventricular assistance, weaning was started and successfully completed with explanation on the 5th day. Two days later the patient died of multiple coronary embolism with thrombosis of the valve. The second case involved a 30-year-old man. Six months before, he underwent surgical procedure with placement of Bio-prosthesis for dissecting aortic aneurysm due to annuloectasia. Upon admission for terminal dilated myocardiopathy, the patient was in kidney failure almost requiring dialysis. Because of this patient's size (Marfan syndrome), no donor heart was immediately available and left circulatory assistance with a Biomedicus pump had to be initiated. The patient lived without mechanical ventilation, in good clinical condition until day 23 when he presented acute right heart failure due to extensive valvular and coronary thrombosis. From these two cases, several important comments can be made about anticoagulation therapy, partial unloading of left ventricle, or need for biventricular assistance, and efficiency of centrifugal devices in these clinical applications.