Abstract

1. The primary effect of strophanthin upon the isolated heart is to increase the force of contraction; in the fresh heart the force of the auricular contraction is increased markedly but force of the ventricular contraction less markedly. In the hypodynamic heart the force of contraction of both auricle and ventricle is increased greatly.

2. The systolic action of strophanthin is opposed by the presence of acid, by the absence of calicum, and by the hypodynamic condition.

3. The action of strophanthin in impairing the rate of conduction is not antagonised, but rather increased by the above conditions. This action, moreover, is not antagonised by any other changes in the ionic content of Ringer.

4. The action of strophanthin upon conduction appears to be largely independent of its action upon contraction.

5. The acids produced by the heart and which accumulate when perfusion is arrested, can be shown to antagonise the systolic action of strophanthin, and this fact explains why hearts, arrested in systole by stropthanthin often relax into diastole, and also why hearts in which the conduction is impaired, before any systolic action has been produced, usually die in diastole and not in systole.