Cardiac nerves arising from the cervical and thoracic sympathetic chain, the vagi, and the recurrent laryngeal nerves of the dog were described. The findings are correlated with the nomenclature of the NA ('66) and proposals of the NAV ('67), and additional suggestions are made when appropriate. Although individual cardiac nerves were followed to specific areas of the heart, additional supplies to these areas were noted from the cardiac plexus. Sympathetic cardiac innervation arose primarily from the vertebral ganglion. Cranial vagal cardiac nerves on the left and caudal vagal cardiac nerves on the right contributed the majority of the parasympathetic cardiac innervation. Right cardiac nerves ramified primarily along the right coronary artery, left descending branch of the left coronary artery, circumflex branch of the left coronary artery on the left surface of the heart, and onto the right atrium. Left heart nerves, in addition to their direct contributions to all but the last area, proceeded along the circumflex branch of the left coronary artery on the caudal and right surfaces of the heart. Right nerves contributed more in the area of the S.A node, while left nerves formed a network in the area of the coronary sinus and A.V. node. Both sympathetic and parasympathetic nerves were followed to each area. It was noted that pulmonary innervation via the cardiac plexus would be disturbed by the technique of cardiac denervation referred to as regional neural ablations.