The great number of open heart operations now performed via the right atrium, makes knowledge of the arrangement of the atrial arteries, particularly the sinus node artery, every important for the surgeon. Although studied by anatomists, little attention has been paid to the surgical significance of these arteries. We have therefore examined the distribution of the right atrial arteries and the course of the sinus node artery in 50 normal adult hearts by classic dissection following, in 30 cases, postmortem angiographic studies. Two major arteries of the right atrium were found to be nearly constant. The anterior artery was present in 96% of the cases and supplied the sinus node artery in 32 cases. Of most surgical significance was the lateral artery found in 90% of the cases. This lateral artery was the principal artery to the free atrial wall and in one case gave rise to the sinus node artery. The well-established preponderance of origin of the sinus node artery from the right coronary system (66%) as opposed to the left (30%) was confirmed. Infrequently, a double supply (4%) was seen. Variability was found in the course of the nodal artery relative to the cavoatrial junction - precaval (58%), retrocaval (36%) or encircling (6%).