A system for filling and subsequently producing inflation and deflation of a balloon-type dilating catheter assembly utilized in performing a percutaneous transluminal coronary angioplasty procedure. Separate primary and secondary fluid pump assemblies are provided for isolating the working pump fluid in the primary assembly from the radiocontrast medium filling the secondary assembly. The primary fluid pump assembly includes a primary pump chamber having a flexible diaphragm forming one wall thereof and a hydraulic cylinder including a piston for supplying fluid under pressure to the pump chamber. The pump assembly has been filled with a relatively incompressible liquid while the piston in the cylinder is held in an intermediate fill position and the diaphragm is held substantially flat to enable the primary fluid pump assembly to produce both convex and concave shapes of the diaphragm as the piston is moved between forward and rearward position. The second fluid pump assembly is adapted to mount to the primary pump chamber. The secondary fluid pump assembly includes a secondary pump chamber having a second flexible diaphragm forming one wall thereof and adapted to mate with the first flexible diaphragm. A resealing fluid entry port is provided in the secondary pump chamber for admitting fluid to the chamber. A bayonet mounting arrangement for mounting the secondary pump chamber to the primary pump chamber is provided to bring the two diaphragms into intimate physical contact. Manual and automatic means for driving the piston of the hydraulic cylinder between forward and backward positions are disclosed to alternately create both balloon-inflating pressure and balloon-deflating vacuum in the secondary pump chamber and dilating catheter assembly by way of the diaphragms after it is filled with a relatively incompressible fluid.