When an artificial blood pump is used in a patient, thrombosis occurs and red blood cells start to accumulate within the interior surface of the blood pump. In a couple of years, this accumulated red blood cells cause serious damages to the pump and therefore patients need to replace their pumps. This study aims to detect the blood viscosity within the heart assist devices and help the experts to get healthy information about possible damages from thrombogenesis. When thrombosis occurs and red blood cells accumulate inside the blood pump, the viscosity of the blood inside the pump starts to increase. In our study, the impeller of the blood pump is improved and thus it does not only rotate but also vibrate with a specific frequency. As the viscosity of the blood starts to increase, the force which is necessary to keep the vibration frequency of the impeller constant starts to increase and therefore phase differences start to happen. Thus, there is a linear relationship between this phase difference and the viscosity of the blood. By capitalizing this relationship, the viscosity of the blood and also ideal replacement time for blood pumps may be determined.