In the following pages an attempt is made to discuss certain aspects of complete heart-block as it occurs in man. While the nervous control of the auricles is well understood, much remains to be discovered regarding the influence of the extrinsic nerve supply to the ventricles. Tn. approaching this problem, the heart, in which the auricles and ventricles are dissociated in their rhythms lends an admirable opportunity for the investigation of its nervous regulation. By the use of certain drugs and other procedures in a series of fourteen cases of complete heart-block, the facts accumulated suggests that the ventricles, despite the presence of complete block, are directly under the control of the parasympathetic and sympathetic systems. The evidence leading to this conclusion is summarised at the conclusion of each section of this report. Electrocardiograms have revealed four distinct disorders of cardiac mechanism over the various phases of the Stokes-Adams syndrome. Two examples of ventricular arrest occurring during partial heart-block are recorded, and two during complete heart-block. In one of these paroxysmal ventricular tachycardia followed by ventricular fibrillation preceded the onset of asystole. This attack was treated by the intra-cardiac injection of 0.5 c.c. adrenalin. The patient recovered.