Action of acetylcholine on bivalve hearts.

The isolated hearts of a comprehensive selection of bivalves were tested to determine the distribution of the excitor and depressor effects of acetylcholine. No broad relationships are obvious although some intrafamily uniformity of response exists. The hearts of most species were both excited and depressed, probably by separate actions of acetylcholine. From these data we can conclude that bivalve heart muscle conforms closely to other molluscan muscle in its pharmacological reactions to acetylcholine.