Which animal has the largest heart?

Purkinje's fibres of the vertebrate heart are modified:

The opening of auricles and ventricles on the right side is guarded by

Where is the Eustachian valve found?

All vertebrates possess a ...$A$.... Fishes have a ...$B$... chambered heart with atrium and ventricles. Amphibians and reptiles have a ...$C$... chambered heart. Birds and mammals have ...$D$... chambered heart.
Choose the correct option.

The first heart sound is associated with which of the following?