Question

“Lub” sound produced during heart beat is caused by
A. Ventricular diastole
B. Ventricular systole
C. Atrial diastole
D. Atrial systole

Answer 1

Hint: The heart has two cardiac cycles, systole and diastole. During systole, the cardiac muscles contract to pump the blood out of the heart. During diastole, the cardiac muscles relax and the heart is refilled with blood. Lub dub is the characteristic sound of the heart beat.

Complete Answer:
- In the cardiac cycle there are four sounds corresponding to the cardiac events.
- The first two sounds are distinguished and have the sound lub dub when heard through a stethoscope.
- There are four chambers in the heart; two ventricles and two atria. The right atria receives the deoxygenated blood from different parts of the body and pumps it to the right ventricle.
- The right ventricle further pumps the deoxygenated blood to the lungs for purification. After purification of blood, the oxygenated or oxygen- rich blood from lungs is received by left atrium and is pumped to the left ventricle for circulation.
- At the beginning of the ventricular systole, the closing action of the mitral and tricuspid valve causes the heart tone ‘lub’.
- At the end of ventricular systole, the closing action of the aortic and pulmonary valve causes the sound ‘dub’.

Therefore the correct answer is (B) Ventricular systole.

Note: The lub sound is heard the loudest at the mitral region of the heart and dub sound is heard the best at the base of the heart. Due to the closure of the atrioventricular valve, the lubb sound is comparatively louder.