In vitro and in vivo evaluation of a right ventricular assist device. A simple right ventricular assist device (RVAD) has been developed. This device will be useful in situations where biventricular failure has been partially treated by placement of a left ventricular assist device, or when right ventricular failure occurs in isolation. This pneumatically actuated, R-wave synchronized, sac type pump contains no valves, and is connected by a graft to the pulmonary artery. The RVAD was tested in a circulation simulator to verify its hemodynamic efficacy and then implanted in six calves for 2-4 weeks to evaluate its biocompatibility. In vitro testing of the RVAD demonstrated that it restored normal hemodynamics in the presence of severe simulated RVF. In six animal implantations, a small amount of thrombus was found in one pump. No anticoagulants were employed. Thrombus was present in the connecting graft in three animals; in two this was clearly related to technical implant errors. No evidence of significant hemolysis was found. This simple RVAD has been found to be hemodynamically effective, is simple to use, and is well tolerated. Refinements in the interconnection graft between the pulmonary artery and the device are necessary. 