$A$ heart murmur occurs due to a defect in:

Given below are two statements.
Statement $I$ - The heart sound $Dub$ is heard during ventricular diastole.
Statement $II$ - The heart sound $Lubb$ is heard during atrial systole.
In the light of above statements,select the correct option given below:

Which nodal fibres lie along the right and left ventricles (interventricular septum)?

The apex beat of the heart is synchronous with:

Systemic circulation of oxygenated blood starts from

Heartbeat can be initiated by