The origin, course and mode of termination of the artery of the sinuatrial node was studied in 45 anatomic specimens by injection-dissection. It was solitary in 88.89% of the cases and double in 11.11%. It arose from the right coronary a. in 64.45% of cases, from the left coronary a. in 24.44%, and from both in 11.11%. The side of origin was not significantly influenced by the coronary dominance. When it arose from the right coronary a., the course of the sinuatrial a. varied greatly with its site of origin from the coronary vessel, either from an atrial a. or from one of its collateral branches, and also depended on its relations with the interatrial septum. When it arose from the left coronary a., its course was relatively uniform, except for arteries arising from the inferior atrial aa., which characteristically involve the posterior wall of the left atrium. Three modes of termination were found: precaval, retrocaval, and in a pericaval arterial circle. These observations made it possible to understand the possible origin of disorders of rhythm observed following disturbance of the arterial supply to the sinuatrial node during certain stages of cardiac surgery, particularly during atriotomies and the surgical correction of certain valvular disorders and congenital malformations, which expose the a. of the sinuatrial node.