Effects of rate and rhythm on contraction of rat papillary muscle

Abstract
The unusual relationship between frequency of contraction and tension developed by the isolated rat papillary muscle has been studied in detail. The progressive decrease in tension with increasing rate is unrelated to the size or weight of the muscle and is not changed by alterations in the ionic composition of the perfusion medium. The force-frequency relationship is also unchanged by addition of plasma, epinephrine or digitalis to the perfusion medium. Rat papillary muscle is similar to other preparations of cardiac muscle with respect to recovery of contractility and the development of rest contractions and postextrasystolic potentiation.

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