Cardiopulmonary interaction is the term that is used to describe the inseparable connection between the heart and lungs. In health, the cardiovascular and pulmonary systems are in perfect balance. In disease, derangements of either system leads to . dysfunction in the other. Physicians attempt to improve health with therapeutic interventions positive pressure ventilation . . typically aimed at treating disease pneumonia with hypoxia in one system lungs with resultant positive recruitment of . . alveoli and negative ventilator induced lung injury consequences and secondary impact on the other system heart with . decreased cardiac output . This manuscript will review the physiologic basis of normal.