A balloon of a balloon catheter is inflated with a liquid inflating medium by a syringe through a flow line. Air in the flow line and the balloon is displaced into a return line. The balloon is deflated by drawing the liquid inflating medium from the balloon along with the air in the return line into the syringe where the air is trapped in the syringe. The balloon is reinflated and deflated by the syringe until the level of air in the liquid inflating medium has been reduced to a predefined level. A first non-return valve and a second non-return valve are provided in the flow and return lines, so that the liquid inflating medium is prevented from flowing from the balloon to the syringe in the flow line and from the syringe to the balloon in the return line.
