Question

the double walled membranous sac enclosing the heart is the
pericardium
endocardium
epicardium
myocardium

Explanation:

The pericardium is a double - walled membranous sac that encloses the heart. The endocardium is the inner lining of the heart chambers, the epicardium is the outer layer of the heart wall, and the myocardium is the muscular middle layer of the heart wall.

Answer:

pericardium