Enhancement of cardiac vagal action during ischaemia of the sino-atrial node.

The effect of ischaemia of the sino-atrial node on cardiac vagal action was studied in anaesthetized dogs. The cut, cardiac end of the right vagus nerve was stimulated with a standard supramaximal stimulus every 10 s. The arterial supply to the sinoatrial node was occluded for periods of 1-3 min during this intermittent vagal stimulation. Vagal action on heart rate was potentiated during ischaemia of the sino-atrial node.