Excerpts from Books and Wikipedia
"In 1025, The Canon of Medicine by the Persian physician, Avicenna, 'erroneously accepted the Greek notion regarding the existence of a hole in the ventricular septum by which the blood traveled between the ventricles.' Despite this, Avicenna 'correctly wrote on the cardiac cycles and valvular function', and 'had a vision of blood circulation' in his Treatise on Pulse.[verification needed] While also refining Galen's erroneous theory of the pulse, Avicenna provided the first correct explanation of pulsation: 'Every beat of the pulse comprises two movements and two pauses. Thus, expansion : pause : contraction : pause. [...] The pulse is a movement in the heart and arteries ... which takes the form of alternate expansion and contraction.'" [Wikipedia: Circulatory system]