An actuator (10) for a heart assist device. The actuator (10) includes an inflatable balloon (12) and a shroud or wrap (14). The inflatable balloon (12) has a first body portion (22), a second body portion (26) and a flexure region joining (24) the first (22) and second (26) body portions. The shroud or wrap (14) is positioned adjacent the first body portion (24) and has a peripheral extent at least equal to the peripheral extent of the balloon flexure region (24). The balloon (12) and the shroud or wrap (14) are shaped such that the shroud or wrap (14) restrains a part of the balloon first body portion (22) at or near the flexure region (24) against displacement towards the shroud or wrap (outward displacement) past a predetermined limit but allows unrestrained displacement away from the shroud or wrap (inward displacement).