Prosthetic valves and their component parts are described, as are prosthetic valve delivery devices and methods for their use. The prosthetic valves are particularly adapted for use in percutaneous aortic valve replacement procedures. The delivery devices are particularly adapted for use in minimally invasive surgical procedures. The preferred delivery device includes a catheter having a deployment mechanism attached to its distal end, and a handle mechanism attached to its proximal end. A plurality of tethers are provided to selectively restrain the valve during deployment. A number of mechanisms for active deployment of partially expanded prosthetic valves are also described.