Cardiopulmonary resuscitation (CPR) in the operating room (OR) is the responsibility of the anesthesiologist who knows the location and function of resuscitation equipment, delegates tasks, and instills calmness in assisting personnel. The algorithms described below have been modified as appropriate for the anesthesiologist in a hospital setting but closely follow the evidenced-based 2010 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care that includes basic life support (BLS), advanced cardiac life support (ACLS), and pediatric advanced life support (PALS). Essential to the swift return of spontaneous circulation (ROSC) after a sudden cardiac arrest (SCA) is defibrillation for ventricular fibrillation (VF) or pulseless ventricular tachycardia (VT), the prompt delivery of effective, minimally interrupted chest compressions to maintain cerebral and cardiac perfusion, and the avoidance of hyperventilation that may cause continued hypotension through a decrease venous return to the heart. Effective compressions deliver oxygen and energy substrates to the myocardium and increase the likelihood that a perfusing rhythm will return after defibrillation. It is important that CPR be resumed immediately after defibrillation without pause for pulse or rhythm checks. When defibrillation terminates VF and ROSC occurs, continuation of chest compressions is often required, since the myocardium has been depleted of oxygen and metabolic substrates and is “stunned.” Table 38.1 lists the classifications for the quality of evidence used to support most of the protocol interventions presented in this chapter.