When the right ventricle contracts,the blood goes into:

The bundle of $HIS$ is a network of which of the following?

The heart beats continuously throughout life without fatigue because.....

Bicuspid and tricuspid valves are attached with inelastic fibres to the papillary muscles in the lumen of the ventricles. These fibres are . . . . . . .

How much of the total blood volume is present in the heart (in $\%$)?

In birds and mammals,the oxygenated blood is received by ...$A$... and deoxygenated blood is received by ...$B$.... The ventricles pump it out without any mixing of oxygenated and deoxygenated blood. Choose the correct option for $A$ and $B$.