After a cardiac operation, there is reversible myocardial dysfunction that also involves a metabolic disorder. In patients with cardiac failure, care must be taken to reduce the strain on the heart by minimizing systemic oxygen uptake, which is, in fact, the main determinant of cardiac output. Inotropic support may improve cardiac output and tissue oxygenation in cardiac failure, but it also increases myocardial stress directly by increasing myocardial demands and indirectly by increasing systemic energy demands. Mixed venous oxygen saturation reflects the balance between cardiac output and systemic oxygen consumption and indicates whether cardiac output can adequately provide the peripheral tissues with oxygen. This physiologic view toward the treatment of postoperative cardiac failure helps us avoid overtreatment, that is, stimulating cardiac output more than necessary for adequate tissue oxygenation. In this way, the strain on the heart can be reduced and myocardial recovery, enhanced.