Question

The “lub” sound (first heart sound) is caused by the

• A. atrial contraction
• B. ventricular contraction
• C. closing of the AV valves
• D. closing of semilunar valves

Answer 1

The correct option is C

closing of the AV valves

"Lub" is the sound of the atrioventricular (AV) or tricuspid and bicuspid valves closing. This occurs at the start of ventricular systole. "Dub" is the sound of closing of the semilunar valves at the root of the aorta and the pulmonary artery. This happens at the beginning of ventricular diastole.