Abstract: A circulation assist method and device is provided wherein the contraction and expansion of a balloon of an IABP system which has already been widespread as a device for pressure support are utilized as power source for operating a pump so as to realize the assist of stream volume. A cylindrical pump chamber is connected at one and the other ends thereof respectively with an inflow hole and an outflow hole. An inflow valve is provided at the side of the inflow hole for permitting blood to stream from the inflow hole into the pump chamber but preventing the backward stream, and an outflow valve is further provided at the side of the outflow hole for permitting blood to stream from the pump chamber into the outflow hole but preventing the backward stream.