During atrial systole,

During atrial systole, atrioventricular valves are open while semilunar valves are closed.

• Atrioventricular (AV) Valves (Tricuspid and Mitral Valves): These valves are open during atrial systole. The open AV valves allow blood to flow from the atria into the ventricles. The tricuspid valve is located between the right atrium and the right ventricle, while the mitral valve is located between the left atrium and the left ventricle.
• Semilunar Valves (Aortic and Pulmonary Valves): During atrial systole, the semilunar valves are closed. The aortic valve is located between the left ventricle and the aorta, while the pulmonary valve is located between the right ventricle and the pulmonary artery. These valves prevent the backflow of blood from the aorta and pulmonary artery into the ventricles.

The coordinated opening and closing of these valves ensure the unidirectional flow of blood through the heart. In atrial systole, the AV valves are open to allow blood to fill the ventricles, and the semilunar valves are closed to prevent the backflow of blood into the ventricles from the major arteries.