Background: In end-stage heart failure, ventricular assist system is necessary to prolong life or as a bridge to transplantation. We had developed a new BiomedlabÒ electro-mechanical implantable ventricular assist device (IVAD) and performed in vivo experiment to evaluate the durability and safety of the device. Methods: We implanted the newly developed IVAD in pre-peritoneal cavity in 4 Hallstein calves. The inflow tract was inserted through left ventricular apex and outflow tract was anastomosed to the descending thoracic aorta. Postoperatively we administered heparin intravenously for 2 days after implantation then administered warfarin sodium daily. We examined serum SGOT, SGPT, BUN, creatinine, LDH, haptoglobin, fibrinogen, whole blood hemogloin, hematocrit, PT, PTT, and plasma hemoglobin, preoperatively and postoperatively.We also recorded the assisting flow rate and hemodynamic parameters of the animals. After IVAD implantation, INR range was monitored and we tried to control INR range about 3.5-4.0. Postoperatively, when we find the device-related problems, we euthanized the animals and performed autopsy. Results: After IVAD implantation, 4 calves lived for 6, 13, 3 and 21 days. Three of them were euthanized due to mechanical problems of electrical shortage, and the other died suddenly due to blood leakage at the outflow tract at postoperative 21 day. Autopsy was performed in all animals and there were no evidences of thromboembolism or hemorrhage in kidney, liver or lungs. There were also no evidences of valve thrombosis or thrombosis in blood sac or inflow/outflow tract. Hematologic and chemical examinations revealed mild hemolysis in the early postoperative period and stabilized with minimal hemolysis. There were no organ dysfunction. Conclusions Newly developed BiomedlabÒ IVAD was feasible for implantation and was functioning well in calf model. Although there were 3 mechanical problems. we did not find any device related thrombosis and serious hemolysis. With this encouraging results, it can be highly possible to perform animal experiments with final version of IVAD after correcting mechanical problems for evaluation of long-term durability and stability.