ABSTRACT
The issue of the first organ developed in the human body has been studied by many scholars, especially in medical science, since a long time ago. The significance of this subject is due to the fact that it can illustrate the developmental process of body structure in a better way. There are three approaches in this regard which consider either the heart, brain, or liver as the first organ to develop in the human body. Avicenna, as a proficient physician who had a comprehensive outlook in his works, recognizes the heart as the first organ to develop in the embryo. He also regards it as a place for a vaporous spirit that acts as an intermediary between soul and body, like an electrical current in the heart. He makes use of experimental evidence based on traditional medicine as well as rational arguments to prove his viewpoint.