A Level Biology Practice Exam 2026 – 400 Free Practice Questions to Pass the Exam

The structure that helps prevent heart valves from turning inside out is the tendinous cords, also known as chordae tendineae. These are strong, fibrous strands that connect the papillary muscles to the atrioventricular (AV) valves (the mitral and tricuspid valves). When the ventricles contract, the pressure inside them increases, pushing the blood against the valves. The tendinous cords ensure that the valves remain tightly closed and do not invert under the pressure, which is essential for maintaining unidirectional blood flow and preventing backflow into the atria.

The myocardium refers to the muscular layer of the heart responsible for contraction but does not play a direct role in valve function. The pacemaker is involved in regulating the heart's rhythm and does not have a structural role in preventing valve inversion. The coronary arteries supply blood to the heart muscle itself and are unrelated to the function of the heart valves. The tendinous cords are crucial for the mechanical stability of the heart valves during the cardiac cycle.