The cardiac and circulatory systems interact on many levels, including mechanical, neurologic, and neurohumoral. The mechanical interactions that are important for the failing heart include effects of intrathoracic pressure and lung volume on venous return and left ventricular function. Recent studies have been directed at exploring the role of mechanical ventilation, continuous positive airway pressure, and systolic gated increases in intrathoracic pressure as cardiac support modes. It appears that in the failing heart improved ventricular ejection predominates over decreased venous return and that both short-term and long-term improvement in cardiac function may be realized. It is also apparent that reflex control of the circulation is altered by respiratory maneuvers and that this may be as or more important than the mechanical effects.