A ventricle assist device comprises an inlet for receiving blood, an outlet for discharging blood, and a chamber disposed between the inlet and the outlet. There is also a means for actuating the ventricle assist device between an expanded configuration and a contracted configuration. In the expanded configuration blood flows into the inlet. In the contracted configuration blood flows out of the outlet. There may be a one-way valve at the outlet for preventing blood flow back into the chamber. The one-way valve is a diaphragm valve. The chamber may have a resilient outer wall. The chamber may have an ovoid shape.