The Effect of Epinephrine on the Myocardium of the Embryonic Chick

Abstract

The myocardium of the embryonic chick heart, before it has been innervated, responds to concentrations of epinephrine as dilute as 1 part in 20,000,000 by an abrupt acceleration in its inherent rate of pulsation. The more slowly the heart beats initially, the more marked is the accelerating effect of epinephrine. Usually the initial acceleration is followed by a period during which the heart slows to a rate intermediate between the initial and the maximal. This deceleration is not due to a decrease in the stimulating effect of the drug applied.