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While it would seem endogenous opioid peptides would reduce pain and heart rate, allowing more time for ventricular filling, there a number of human studies suggesting EOP levels do not correlate with blood pressure, heart rate, and central venous pressure in cases of myocardial infarction. On the contrary, animal studies suggest endorphins may augment ischemic damage during MI, and in animal models of circulatory shock and heart failure opioid receptor blockade has been shown to improve hemodynamic parameters and survival rates.