What leads to constrictive pericarditis?

Infections and other: This is a stiffening of the normally pliable sac that holds the heart. Infections in the fluid around the heart, and scarring conditions that have no known cause can cause this sac to stiffen and this results in incomplete filling of the heart between beats. This lack of filling can lead to heart failure, as the heart is incapable of pumping blood as efficiently. It is a rare condition.