Complex sentence: Cardiac muscle tissue or myocardium forms the bulk of the heart as part of the three layered structure of the heart wall-the inner endocardium, middle myocardium and outer epicardium.
Split into simpler sentences: Cardiac muscle tissue or myocardium forms the bulk of the heart. The heart wall is a three layered structure with a thivk layer of myocardium sandwiched between the inner endocardium and the outer epicardium.