Based on the study often hearts of human embryos from the Orts Llorca collection in Madrid, comprising stages 12–17 of O’Rahilly, the origin ofthe septum primum was analyzed. The septum referred to has its origin in the dorsocaudal part of the common auricle starting from the cells of the lower cushion which makes contact with the wall of the auricle referred to. The closure of the atrioventricular canal is due to the introduction of the spina vestibuli of the septum primum between the two endocardial cushions. The foramen primum is formed in the human species in the same way as in the rest of the most highly developed vertebrates.