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While functional cardiac changes and myocardial pathology have been associated with shock avoidance, whether these effects arc due to shock alone or other aspects of the avoidance situation has not been determined. With 6 groups of “yoked‐chair” squirrel monkeys. electrocadiogram, blood pressure, and myocardial pathology were studied. Each avoidance monkey was paired with a yoked monkey which could not cope with shock and received each delivered to the avoidance monkey. The effect of this stress was observed in 5 of 6 yoked monkeys u physical deterioration and severe bradycardia with ventricular arrest, but no significant myocardial necrology. With one exception, paired avoidance monkeys showed no effect of stress. Since previous research has shown that the avoidance situation induces a sympathetic activation which is manifested as myofibrillar degeneration and the present in experiment demonulraled that the yoked situation elicits a parasympathetic‐like response and bradycardia with ventricular arrests. cardiac response to the stress of shock avoidance varies depending on whether it occurred in the avoidance or yoked situation.