In clinical settings, quick application systems with easy access for circulatory support are desired. For left heart assist, an intraarterial axial flow pump (Hemopump) has been developed and applied to clinical cases. However, no simple way has been proposed for right heart assist. We have developed an intravenous axial flow pump for temporary right heart assist and have reported its hemodynamic effect. In this study, in vivo evaluation of this system was performed. The pump system consists of an outflow cannula, an impeller that was newly developed for intravenous use, and a driving system for the Hemopump. A prototype pump demonstrated 3.2 L/min of maximal flow at a pressure differential against 40 mmHg at a pump speed of 28,000 rpm in mock circulation. Application to goats is as follows. A 14 mm low porosity graft was anastomosed to the infrarenal inferior vena cava (IVC). The pump system was inserted into the IVC through the graft and advanced to the right heart using balloon catheter guidance under fluoroscopy, and the tip of the cannula of the pump was positioned at the main pulmonary artery. In acute experiments, this system provided effective right heart assist under induced pulmonary stenosis and induced biventricular failure with left ventricular assist. Chronic animal experiments were performed for as long as 4 hr using adult goats weighing 51-54 kg. There were no difficulties in pump insertion. In one goat, the drive shaft was broken because of kinking of the shaft inside the body, caused by failure in securing the pump. Levels of platelet counts and plasma hemoglobin were acceptable, and there was no prominent damage to heart tissues. In conclusion, an intravenous axial flow pump introduced through a peripheral vein is practicable for temporary right heart assist.