A system for improving cardiac output of a patient suffering from pulseless electrical activity or shock and yet displays myocardial wall motion including: a sensor to detect myocardial activity to determine the presence of residual left ventricular pump function having a contraction or ejection phase and a filling or relaxation phase, a device to prompt the application of or apply a compressive force repeatedly applied to the chest based on the sensed myocardial activity such that the compressive force is applied during at least some of the ejection phases and is ceased during at least some of the relaxation phases to permit residual cardiac filling, thereby enhancing cardiac output and organ perfusion.