What is the membrane surrounding the heart called?

Heart murmurs are indicative of a defect in which of the following?

Which structure first generates an action potential?

Following are the stages of the pathway for the conduction of an action potential through the heart:
$A.$ $AV$ bundle
$B.$ Purkinje fibres
$C.$ $AV$ node
$D.$ Bundle branches
$E.$ $SA$ node
Choose the correct sequence of the pathway from the options given below:

Give the location of the tricuspid valve.

Which animal has the largest heart?