If necessary, initiate cardiopulmonary resuscitation (CPR). Other than maintaining cardiac output, CPR may also serve to break large air bubbles into smaller ones and force air out of the right ventricle into the pulmonary vessels, thus improving CO. Even without the need for CPR, this rationale holds for closed-chest massage. Animal studies have shown that the benefit of cardiac massage equals that of left lateral recumbency, as well as intracardiac aspiration of air.