Abstract

The effects of five cations on the electrogram and myogram of mammalian heart muscle were studied, using the papillary muscle preparation. Increasing potassium concentration produced an inversion of the T deflection, widening of the R deflection and diminution of systolic force. Removal of potassium resulted in a repetitive response to each electrical stimulus. Ammonium ion increased contractile force, and widened the R deflection and the R-T interval.

Increasing the concentration of calcium increased the force of contraction and inverted the T deflection. Decreasing the concentration of calcium decreased the force of contraction without affecting the electrogram until, at a calcium level at which no contractile force could be recorded, the R-T interval decreased, and the R-T segment became elevated.

Strontium added to a solution containing the usual amount of calcium had an effect indistinguishable from that produced by adding an equimolar amount of calcium. However, when strontium was added to a solution low in calcium, it produced widening of the R-T interval and prolongation of systole. These effects were abolished by adding calcium.

Magnesium had no demonstrable effect on either myogram or electrogram.