Why are pig's hearts used in most heart transplants involving human recipients? Name the complications observed in using pig's heart for transplant.

First to clarify, pig hearts are not used in humans where
a transplant is required. There have been a couple of reported attempts to do the same,
but they have failed due to the pig's organ being rejected by the human immune
system.

Though the pig's heart is very similar in anatomy,
function and structure to the human heart it is not a perfect match. Scientists are
conducting studies to use stem cell research to make the pig heart totally compatible
with that of the human. This will not lead to their being rejected by the immune system
and also ensure that they are a perfect fit to the requirements of the human
body.