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An implantable Left Ventricular Assist Device (LVAD) is used as a Right Ventricular Assist Device (RVAD) because there is no implantable blood pump specialized for a right ventricular assist. As a demanded pump head of the implantable RVAD is different from that of LVAD, LVAD used as RVAD is operated at off-design points. In the operation of blood pumps at offdesign points, hemolysis (destruction of blood cells) and thrombosis (formation of blood clots) can occur. As a realization of the implantable RVAD specialized for a right ventricular assist has been expected due to these backgrounds, the implantable RVAD has been developed by our research group. In the present study, motions of the impeller in a developed RVAD were investigated to clarify a floating mechanism of the impeller supported by dynamic pressure bearings. In experiments, performance tests of RVAD were carried out and motions of the impeller were measured by using two laser displacement sensors. As a result, it was confirmed that a main motion of the impeller was a whirling motion and its frequency was a rotational frequency of the impeller. The amplitude of the whirling motion was about 0.2 times as large as a mean radial clearance of bearings.

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