In tests on guinea pig hearts in situ asphyxia tolerance was found to be increased early in hemorragic shock four times control value. These results are suggestive of an energy saving mechanism in shock whereby the heart is not damaged out metabolically relieved. Myocardial analyses showed that, owing to shock-related cardiac relief, under a simultaneous asphyctic stress the intracellular potassium stock decreases later and markedly less.