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Patterns of arterial supply to the atria were studied with respect to the coronary sinus region in 60 human hearts obtained from patients with a negative cardiac history and in 2 hearts with ECG-demonstrated coronary sinus rhythm. The atria, including the interatrial septum, were supplied by the right (40%) or left (30%) or both (30%) sinuatrial arteries which, however, did not reach as far as the posterior margin of the oval fossa and the coronary sinus. The region of the coronary sinus with the Eustachian ridge received direct branches from the trunk of the right (41%) or left (11%) coronary artery or both (48%) in the adjacent part of the coronary sulcus. Possible development of the 'coronary sinus rhythm' on the basis of multifocal damage of the sinuatrial arteries is discussed.

The lymphatic and venous bed was evaluated in 42 human heart papillary muscles. The lymphatics form networks in the superficial and deep layers of the subendocardium and in the myocardium of the papillary muscles. In the apical area, the subendocardial lymphatics gradually merge with the fine myocardial, developing arcades at the origins of chordae tendineae. Thicker myocardial lymphatics leave the area passing along the connective tissue septa, often in close vicinity to the blood vessels. The injection method failed to reveal deep lymphatics in the connective tissue of chordae tendineae. Lymphovenous anastomoses were disclosed in the papillary muscle. The possible morphological pathways for lymphatic drainage of the papillary muscle are as follows: (1) the lymphatic bed subendocardial and myocardial, joining on the ventricular wall bed at the muscle base, and (2) lymphovenous anastomoses, passing along from the myocardial and subendocardial lymphatic bed into the ventricular wall veins and the sinus coronarius system, or into the thebesian veins and further directly into the heart ventricles.

The arterial supply to the region of the coronary sinus and the interatrial septum was examined in 18 normal canine hearts. In 13 of a further 18 dogs, coronary sinus rhythm was evoked by the ligation of atrial arteries, subsequent to which the arteries were visualized by injection of latex. A stable coronary sinus rhythm is evoked by producing ischaemia in an extensive area of the right atrium, including the sinus node, the interatrial septum and Bachmann's bundle, but preserving from ischaemia the posteroinferior part of the right atrium. Microscopical examination of the hearts with coronary sinus rhythm, and comparison with 9 control hearts, failed to demonstrate any morphological centre, in the form of nodal cells, which might have been responsible for the abnormal rhythm. In the posterior part of the right atrium, the ischaemic changes failed to affect the approaches of the atrioventricular node. The approaches were predominantly composed of cells poor in myofibrils mixed to a variable degree with cells of the working myocardium. We discuss the possibilities of the development of coronary sinus rhythm and "circus movement" with regard to the participation of the approaches to the atrioventricular node.