The heart is in good hands.

A review of mechanical cardiopulmonary interactions is presented and some extrapolations are made concerning cardiopulmonary resuscitation, with the following conclusions: (1) The cardiac fossa of the lungs provides a soft heart bed at normal lung volumes, but tenses at higher volumes to improve the support of the heart during postural changes. (2) The cardiac fossa is a physiologic constraint at normal heart volumes. It acts to restrict ventricular expansion before there is pericardial restriction. The physiologically useful interventricular interdependence is thereby promoted. (3) The effect of lung inflation in tensing the walls of the fossa may also sometimes embarrass both ventricles. Together with the raised intrathoracic pressure, it is responsible for the fall in left and right ventricular volumes and output during positive pressure ventilation. (4) New techniques of cardiopulmonary resuscitation depend on repeated, abrupt increases in pressure in both chest and abdomen, as in coughing.