A system and method for cardiac assist of a heart. The system comprises a catheter on which is mounted an inflatable balloon configured for inflation inside a ventricle. The system preferably includes a fluid pump and a processor configured to activate the pump to inflate the intra-ventricular balloon in the ventricle during a predetermined first phase of the cardiac cycle and to deflate the balloon during a predetermined second phase of the cardiac cycle. The predetermined first phase may be the end of the slow ejection phase corresponding to the ascending part of the T wave, and the predetermined second phase may begin at the peak of systolic augmentation resulting from inflation of the balloon which corresponds to the descending part of the T-wave. The method of the invention includes delivering the balloon to a ventricle of the heart and transiently inflating the balloon to achieve a predetermined intra-ventricular systolic pressure.