Ventricular assist device is used as a bridge to heart transplantation and heart disease. Among them, knowing the status of the ventricular assist device when implanted in the body pneumatic pulsatile ventricular assist devices is important. This is because when the velocity of blood flow through the ventricular assist device is slow, there is a possibility that a thrombus occurs and thrombosis at risk fatal to the patient. In order to grasp the state of a ventricular assist device, it is necessary to implant the various sensors. At this time, since there is a problem of infection and management of the sensor, in this study, we estimate the state of a ventricular assist device indirectly via the pressure of the air tube that can be measured in in vitro. And we were compared to the in vitro experimental results. As a result, the estimated value and the measured value was some errors, however it is believed that it can be possible to improve the accuracy by using a refinement of the estimation process, to minimize the problem of infection.