A Study of one hundred hearts (adults 56, children 44) has been made. The S-A mode arteries and A-V node arteries are measured and analysed. The chief results are as fo11ows: (1) 67% of S-A node arteries originated from the right coronary artery; 33% arose from the left coronary artery. A number of the S-A node arteries arising from the right coronary artery were the continuation from the anterior right atrial branch. Occasionally, they may be come from the intermediate right atrial branch or intermediate left atrial branch. (2) The distance between the right S-A node artery origin and the aortic root was about 1.28?0.12 cm in adults, and 0.85?0.09 cm in children, while between the left S-A node artery origin and the bifurcation of the left coronary artery, it was about 0.84?0.19 cm in adults and 0.41?0.03 cm in children. The external diameters of the S-A node arteries were measured. The mean value was as follows: 0.17?0.01 cm (adults); 0.12?0.01 cm (children). (3) The relation between the origins of S-A node artery and A-V node artery may be divided into six types. ①The S-A node artery and A-V node artery which originated from the right coronary artery were about 58.06%. ②The S-A node artery arising from the left coronary artery and the A-V node artery originating from the right coronary artery occurred in 30.11% ③The S-A node artery originated from the right coronary attery, while the A-V node artery arose from the left. This condition was about 6.45%.④The type that the S-A node artery arose from both coronary arteries, and the A-V node artery originated from the right was about 3.22%.⑤Both the S-A node artery and A-V node artery arising from left coronary artery occurred in 1.08%.⑥The A-V node artery originating from the left and right coronary arteries, and the S-A node artery arising from the right coronary artery were about 1.08%.