THE EFFECT OF INDUCED FAILURE AND DIGITALIZATION ON THE EXCITABILITY AND RHYTHMICITY OF THE DOG'S HEART

¹ Department of Physiology and Pharmacology, State University of New York, College of Medicine at New York City, Brooklyn, N. Y.

1) The effect of ouabain on the excitability, conductivity and refractory periods of the in situ dog auricle and ventricle has been determined.

2) Heart failure was produced by ligation of the aorta in open-chested dogs. Measurements were made before ligation, at intervals after ligation as failure progressed and during the period of maximum therapeutic effect of ouabain.

3) No significant changes in thresholds to stimulation, conduction times, refractory periods or the ability to respond to high driving rates were found in either the auricle or the ventricle during the periods of:

a) Maximum force of contraction shortly after ligation,

b) Failure,

c) Improved force of contraction after ouabain.

4) The suggestions are made that the extravagal slowing action of the cardiac glycosides may derive from a direct effect on the pacemaker of the heart, and that their action on the rate of the heart is to some extent independent of their action on the force of contraction.