A modular prosthetic valve device for implantation in a patient and a system for and method of delivering such a modular valve device and assembling it in vivo are disclosed. The valve device is designed as two or more modules to be delivered unassembled, spatially separate, and combined into an assembled valve device in the body at or near the site of implantation. The valve device of the invention is deliverable as modules, providing a smaller delivery diameter than pre-assembled percutaneous valves, permitting use of a delivery device of reduced diameter, and increasing the flexibility of the valve device during delivery, compared to percutaneous valve devices in the art. The modules of the valve device may be connected by pull wires for delivery sequentially, and then assembled by remote manipulation using the pull wires. Various locking mechanisms are provided for attaching the device modules together.