<P> The tendon of Todaro is a continuation of the Eustachian valve of the inferior vena cava and the Thebesian ring of the coronary sinus . Along with the opening of the coronary sinus and the septal cusp of the tricuspid valve, it makes up the triangle of Koch . The apex of the triangle of Koch is the location of the atrioventricular node . </P> <P> During atrial systole, blood flows from the atria to the ventricles down the pressure gradient . Chordae tendineae are relaxed because the atrioventricular valves are forced open . </P> <P> When the ventricles of the heart contract in ventricular systole, the increased blood pressures in both chambers push the AV valves to close simultaneously, preventing backflow of blood into the atria . Since the blood pressure in atria is much lower than that in the ventricles, the flaps attempt to evert to the low pressure regions . The chordae tendineae prevent the eversion, prolapse, by becoming tense thus pulling the flaps, holding them in closed position . </P> <Ul> <Li> <P> Papillary muscles and chordae tendineae </P> </Li> <Li> Play media <P> Ultrasound showing redundant chordae tendineae </P> </Li> </Ul>

Valve responsible for preventing backflow of blood from the lungs into the heart