The human heart lies in the space present between the two lungs,which is called . . . . . . .

When the heart of a frog is removed,it will:

Heartbeat can be initiated by

Select the correct option:
$(1)$ The pericardium is a double-layered membrane surrounding the heart.
$(2)$ The $SA$ node has a higher rate of impulse generation compared to the $AV$ node.

The human heart is derived from which germ layer?

What does a heart murmur indicate a defect in?