Final answer:
The atrioventricular (AV) valves, including the tricuspid and mitral or bicuspid valves, are passive elements that control blood flow between the atria and ventricles based on pressure changes within the heart chambers.
Step-by-step explanation:
The atrioventricular (AV) valves are passive structures in the heart that play a critical role in the one-way flow of blood. They include the tricuspid valve on the right, which is located between the right atrium and ventricle, and the mitral or bicuspid valve on the left, located between the left atrium and ventricle. These valves open passively when the pressure in the atria exceeds the pressure in the ventricles, such as during the relaxation phase of the heart (diastole), allowing blood to flow from the atria to the ventricles. When the ventricles contract (systole), the pressure rises in the ventricles, which leads to the closure of the AV valves to prevent backflow of blood into the atria. This action is aided by the chordae tendineae and papillary muscles which prevent the valves from inverting.