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Cardiac contractility was determined during progressive hypothermia in intact anesthetized dogs by attaching a strain gauge arch directly to the left ventricle. A threefold increase in contractile force was observed as the rectal temperature fell to 25°C. Below this temperature a gradual reduction in amplitude of contraction occurred. Neither a decrease in diastolic interval nor circulating blood volume influenced the augmented contractile force. A similar increase in force of ventricular contraction resulted when the isolated perfused rabbit heart was cooled. The data suggest that cold per se exerts a positive inotropic action on cardiac muscle.
Covino et al. (1958) studied this question.