epimyocardium

noun, plural ep·i·my·o·car·di·a [ep-uh-mahy-uh–kahr-dee-uh] /ˌɛp əˌmaɪ əˈkɑr di ə/. Embryology.

1. the outer, mesodermal layer of the embryonic heart, which develops into the epicardium and the myocardium.