Energetics of isovolumic contractions of the isolated rabbit heart.

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Abstract
In isolated beating rabbit hearts, the heat production (measured by Dewar-flask calorimetry) and O2 consumption (measured polarographically) increased in a similar way to force development (assessed as the time integral of left ventricular developed pressure) when the diastolic size of the heart was increased. The energy expenditure of the heart consists of an element which is independent of the force developed and another which varies with the force developed. The calorific equivalent of O2 in the beating heart when it was provided with pyruvate as a substrate was 20.48 mJ/.mu.l:O2 at 25.degree. C. The anaerobic metabolism was well below 5% of the total energy liberation and was constant at all levels of mechanical activity.