The HeartMate II is a high speed, electric, axial flow, rotary blood pump. The pump drains blood from the left ventricular apex via a rigid inlet cannula and ejects into the aortic root via an outflow cannula joined to the aorta with an end to side anastomosis. Power and control of the pump are delivered through a percutaneous cable from the pump to the belt-worn System Driver. Patient outcomes will be compared to objective performance criteria based on historical data from other Thoratec implantable ventricular assist devices.