Cardiac catheterization is conducted using a probe having a balloon assembly, in which a spring has a resting axially elongated configuration and a torsed, axially shortened configuration. An inflatable balloon is twisted about the spring and mechanically linked to the spring. A flexible sheath is disposed about the spring within the balloon, the sheath and the wall of the balloon defining a chamber to contain a fluid flowing therein and thereout for inflation of the balloon and deflation of the balloon so as to energize and de-energize the spring.