Excitability and Refractory Period of Isolated Heart Muscle of the Cat

Abstract

Auricles and papillary muscles were suspended in Locke''s soln. By means of a dual pulse square wave generator and oscilloscope recording, the refractory period and excitability were measured. The auricles were less excitable and had shorter refractory periods than the papillary muscle. No relationship between the level of resting excitability and refractory period was found to exist. Mechanical systole and refractory period are closely related especially for the papillary muscle. Wide changes in rate of stimulation and temp. of the bath did not alter resting excitability. The refractory period shortened with increases in rate in an exponential manner. Increases in temp. shortened the refractory period in a linear relationship. A shift in pH towards acidity lowered resting excitability and lengthened the refractory period. At temps. below 27[degree]C, papillary muscle was capable of summation and tetanus. The isolated auricle was capable of fibrillation following a single shock put in at a point just beyond the absolute refractory period.