Abstract

In the vagotomized, anesthetized dog and the open-chest preparation, ouabain increases the sinus bradycardia produced by maximal vagal stimulation at frequencies of 15 per sec. or more, but not at 10 per sec. or lower.

In the decentralized canine heart, ouabain increases the A-V block produced during rapid atrial stimulation by vagal stimulation at frequencies of 5 or 10 per sec.

In the dog heart-lung preparation, ouabain sensitizes both the S-A node and the A-V node to acetylcholine.

These results confirm the findings of Boehm (1872) and Gremels (1935) that ouabain sensitizes the heart to vagal stimulation.