AbstractThe principal intrinsic ganglion sites in the human infant's heart have been described. They are arranged in six main groups. While most ganglia are associated with the atria, ventricular neurons have also been identified and their significance regarding possible ventricular parasympathetic innervation is discussed. The ganglia vary considerably in size, with most of the larger ones lying on the superior aspect of the heart near the superior vena cava, the aorta and pulmonary artery. They all possess well‐defined capsules. Most of the contained neurons appear to be multipolar, but pseudounipolar and occasional bipolar forms have been detected. Two plexuses exist in the parietal pericardium. Large complicated nerve endings described by previous writers have not been identified, but free endings might exist. Networks in the subepicardium, subendocardium and associated with the coronary arteries have been demonstrated and their functional significance is discussed. Nerve endings, either simple or complicated, were not seen in relation to these plexuses in this investigatio