Arterial supply to the sino-atrial and atrioventricular node is studied after coronary RHODOPAS injection on 15 adult hearts taken off during autopsy. Both coronaries were injected in 7 cases, left ostium in 2 cases and the right on in 6 cases. The sino-atrial node is supplied by the right sino atrionodal artery (S.A.N.A) in 6 cases upon 7 and in 3 cases by the left S.A.N.A. Anastomoses exist in 2 cases between the right S.A.N.A. and the left S.A.N.A. The atrio-ventricular nodal artery arises from the retro-ventricular trunk branching from the right coronary artery mainly. The authors emphasize that care must be taken to protect the vascular supply to the conduction tissue during cardiac surgery.