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The monoaminergic innervation of the coronary vessels and myocardium in the dog was studied by means of the histochemical fluorescence method. The distribution of monoaminergic terminals in the arterial wall depends on the diameter of the artery. In large arteries, the terminals are regularly distributed around the entire circumference, the fibres being situated between the elastic lamellae of the adventitia. The terminals within the media could not be detected. In small arteries, the sympathetic ground plexus aggregates in two parallel strands, the artery being between them. In arterioles, two thick fibres only accompany the vessel. The myocardium is innervated by means of a three-dimensional sympathetic ground plexus distributed between the myocardial cells independently of vessels. No difference in density of innervation was found between the right and left heart. The point-counting method, on the other hand, has revealed that the density of innervation in the left auricle is nearly twice as dense as in the left ventricle. The terminals innervating the myocardium are markedly thinner than the fibres innervating the arteries. Two-dimensional plexuses innervate the epicardium, endocardium and valves.

The remnant stumps of the atria in six calves surviving with the artificial TNS-Brno II methacrylate heart for up to 5 months were examined by means of the Bodian silver-impregnating technique and by the formalin-induced fluorescence technique visualizing noradrenaline in monoaminergic nerve terminals. The degeneration of the nerve terminal system detected in animals surviving for 2 days and 1 week was followed by regeneration of the vegetative nerve system in four animals surviving for greater than 1 month. Moreover, thick myelinated nerves afferent in character were detected within the atrium of one animal surviving for 5 months.

The monoaminergic innervation of the coronary vessels and of the myocardium in dogs was examined by means of degenerative techniques: (i) local perivascular neurotomy was performed at the origin of the left coronary artery; (ii) the stellate ganglion was removed bilaterally. Evaluation of the neural degeneration pattern led the suggestion that three types of neurons at least exist within the heart: (i) neurons innervating the coronary vessels both in the ventricles and in the atria; (ii) neurons innervating the ventricular myocardium, and (iii) neurons innervating the atrial myocardium. The post-ganglionic fibres of the stellate ganglion innervate the vessels of the whole heart. Their contribution to the innervation of the ventricular myocardium represents about 30%.