A heart-assist system and a method for operating same are described in which a pump is connected to a ventricle to receive output therefrom. An actuator operates to cause the pump to conduct a fill cycle in which it receives output from the ventricle to which it is connected, and to conduct an eject cycle in which the contents of the pump are expelled. The time of initiation of at least one of the fill cycle and the eject cycle is varied in relation to systole of the ventricle to which the pump is connected to thereby vary the loading of the ventricle. Several techniques for detecting termination of systole are described including a compliant stop on the pump.