The developmental study on the third coronary artery of human being.

The 3rd coronary artery, whose anatomical significance is defined, is a normal variant of the conus branch of the right coronary artery. This study involved the stereoscopic comparative investigation of human fetal hearts from 13 to 40 weeks of age and human adult hearts from 18 to 88 a of age. The incidence of the 3rd coronary artery in human fetuses was 45 out of 218 or 20.6%. No clear sexual differences were observed. Anastomoses had already developed between the 3rd coronary and the branches of the left anterior descending artery during the fetal stage. The 3rd coronary artery orifices in human fetuses was located at 9 o'clock (+/- 0 degree) most frequent (48.9%), and at 8 o'clock (-30 degrees) most infrequent (22.2%). The incidence of the 3rd coronary artery in human adults was 36.8%. In the human adult's normal group, the orifice was located at 9 o'clock (+/- 0 degree) most frequent (59.0%), and at 8 o'clock (-30 degrees) most infrequent (14.8%), while on the other hand in the pathologic group, the orifice was located at 9 o'clock (+/- 0 degree) most frequent (54.9%) and at 10 o'clock (+30 degrees) most infrequent (11.5%). Further, multiple 3rd coronary artery orifices, which were not observed in human fetal hearts, were observed in the human adults' heart. Furthermore, the existence of multiple orifices and the fact that human adult hearts had a higher incidence than human fetal hearts suggests the possibility that the 3rd coronary artery develops after birth.