Functional anatomy of the canine mediastinal cardiac nerves located at the base of the heart.

The major canine cardiopulmonary nerves which arise from the middle cervical and stellate ganglia and the vagi course toward the heart in the dorsal mediastinum where they form, at the base of the heart dorsal to the pulmonary artery and aorta, the dorsal mediastinal cardiac nerves. In addition, the left caudal pole and interganglionic nerves project onto the left lateral side of the heart as the left lateral cardiac nerve. These nerves contain afferent and (or) efferent axons which, upon stimulation, modify specific cardiac regions and (or) systemic pressure. In addition, with the exception of the left lateral cardiac nerve, stimulation of each of these nerves produces compound action potentials in the cranial ends of the majority of the major cardiopulmonary nerves demonstrating that axons in each dorsal mediastinal cardiac nerve interconnect with axons in the majority of the cardiopulmonary nerves. Axons in the left lateral cardiac nerve connect primarily with axons in the left caudal pole and left interganglionic nerves. The dorsal mediastinal nerves project distally onto the heart as coronary nerves accompanying the right or left coronary arteries. These innervated the ventricular myocardium which is supplied by their respective vessels. The left lateral cardiac nerve projects directly onto the lateral epicardium of the left ventricle. The dorsal mediastinal and left lateral cardiac nerves are the major sympathetic cardiac nerves. Thus, the cardiac nerves located in the mediastinum at the base of the heart are not simple extensions of cardiopulmonary nerves, but rather have a unique anatomy and function of their own.