There are several clinical controversies derived from the discrepancy on the description and relations of the coronary arteries in human hearts of either sex and in different races. OBJECTIVE--To study the clinical and surgical importance of the variations of the origin of the artery of the sinoatrial node in hearts of human individuals. MATERIAL AND METHOD--Normal hearts of cadavers of 100 individuals (31 females and 69 males), belonging to 24 Caucasians (whites) and 36 non-Caucasians (Negroes and Mulattoes), whose age varied ranged from 7 to 80 years, were studied. The coronary arteries were injected with gelatin mixed to a radiopaque substance (Cylatrast) and a red or blue pigment. RESULTS AND CONCLUSIONS--1) The artery of the sinoatrial node was originated more frequently from the right coronary artery (58%) than from the left. 2) When originated from the left coronary artery the artery of the sinoatrial node was more frequently a branch of the circumflex artery (30%) than from the trunk of the artery (12%). 3) No sexual or racial factor influenced the anatomical variations. 4) The most frequent arteries originating the artery of the sinoatrial node were the right anterior medial atrial artery and the left anterior medial atrial artery. 5) No cases of blood supply to the sinoatrial node were found originating neither from other arteries than the coronary arteries nor from both coronary arteries. 6) The distribution of the coronary arteries allows to understand the possible ischemic etiology of the sinusal node syndrome and permits to the surgeon a safe approach to cardiac disease.