Serial sections of rat heart and adjacent organs including large vessels and trachea were made and the distribution of cardiac ganglia was investigated by a drawing reconstruction method. The following results were obtained. 1) Cardiac ganglia were not found at the peripheral region of aorta and arch of aorta. 2) They were not found at the bifurcated region of the trachea, but small ganglia were distributed around the bronchi. 3) Small ganglia were also observed in the wall of pulmonary artery distal to the bifurcasion. 4) Many ganglia of different sizes were gathered in the region between the conflux and the opening of pulmonary vein. 5) They were not observed in either atria or ventricles, anuli fibrosi and the impulse conducting system. The comparative anatomy of the distribution of cardiac ganglia in other mammals was discussed.