A self-contained and hand-held power-assisted syringe is provided which is suitable for the controlled injection of fluid material during medical procedures such as coronary angiography procedures which utilize small-bore and small sized guide catheter systems. The present invention provides a greater degree of injection power on-demand than was previously possible in a portable and hand-held syringe; and it can deliver larger volumes of radiopaque contrast medium at greater pressures than was previously possible using a conventional manual syringe. The power assisted syringe, along with all components necessary for its effective use and operation, may be pre-packaged and steriled within a single container and then disposed of after use.