thought or invisible pores as Galen thought. The blood from the right chamber must flow through the vena arteriosa (pulmonary artery) to the lungs, spread through its substances, be mingled there with air, pass through the arteria venosa (pulmonary vein) to reach the left chamber of the heart, and there form the vital spirit....Saints and saviours of Islam, By Hamid Naseem Rafiabadi, p. 295 Elsewhere in this work, he said: The heart has only two ventricles...and between these two there is absolutely no opening. Also dissection gives this lie to what they said, as the septum between these two cavities is much thicker than elsewhere. The benefit of this blood (that is in the right cavity) is to go up to the lungs, mix with what air is in the lungs, then pass through the arteria venosa to the left cavity of the two cavities of the heart; and of that mixture is created the animal spirit. Coronary circulation Ibn al-Nafis also postulated that nutrients for heart are extracted from the coronary arteries: Again his [Avicenna's] statement that the blood that is in the right side is to nourish the heart is not true at all, for the nourishment to the heart is from the blood that goes through the vessels that permeate the body of the heart. Capillary circulation Ibn al-Nafis had an insight into what would become a larger theory of the capillary circulation. He stated that "there must be small communications or pores (manafidh in Arabic) between the pulmonary artery and vein," a prediction that preceded the discovery of the capillary system by more than 400 years. Ibn al-Nafis' theory, however, was confined to blood transit in the lungs and did not extend to the entire body: For this reason the arterious vein has solid substance with two layers, in order to make more refined that (the blood) which transsudes from it. The venous artery, on the other hand, has thin substance in order to facilitate the reception of the transsuded [blood] from the vein in question. And for the same reason there exists perceptible passages (or pores) between the two [blood vessels]. Pulsation Ibn al-Nafis also disagreed with Galen's theory that the heart's pulse is created by the arteries’ tunics. He believed that "the pulse was a direct result of the heartbeat, even observing that the arteries contracted and expanded at different times depending upon their