The research group of Terumo Corporation, NTN Corporation, and the Setsunan University have been developing an implantable left ventricular assist system (T-ILVAS) featuring a centrifugal blood pump with a magnetically suspended impeller (MSCP). The present study describes results of chronic animal experiments using the MSCP. The MSCP has been tested ex vivo and in vivo in 6 sheep as a left heart bypass between the left ventricular apex and descending aorta. Ex vivo chronic sheep experiments using Model I demonstrated long-term durability, nonthrombogenicity, low hemolysis (<6 mg/dl), and excellent stability of the magnetic bearing with long-term survival for up to 864 days. Average pump flow rate was 4 L/min at a fixed rotational speed of 2000 rpm. Power spectral analyses of heart rate, aortic pressure, and blood temperature maintained normal 1/f fluctuation during the study. The retrieved pump was completely free from thrombus formation and there was no evidence of infarct in major organs. The implantable Model II was evaluated ex vivo in two sheep and intra-thoracically implanted in a sheep. These experiments were terminated at 70, 79, and 17 days due to blood leakage through the connector system within the housing. No thrombus formation was observed in any of the retrieved pumps. A modified Model II with a new connector system was subsequently intra-thoracically implanted in a sheep. The sheep survived for 482 days without any sign of thromboembolic complication or hemolysis at a fixed rotational speed of 1700 rpm and an average pump flow rate of 5 L/min. There was no intra-device thrombus formation or infarct in major organs. The Model III system, consisting of an implantable controller and a new MSCP with a reduced input power of 13 W, has been developed and implanted in a chronic sheep model. The MSCP was implanted in the left pleural space and the controller in the abdominal wall. The experiment is still in progress for more than 30 days without any significant complication to date. These animal studies strongly suggest the feasibility of the MSCP for use as long-term circulatory assist.