What does the heart consist of or what is it mostly made up of?
Heart is myogenic. Means formed of cardiac muscles.
Heart is covered externally of pericardium This is connective tissue layer keeping its shape constant.
The inner side of heart is lined with endothelium. The endothelium is in continuous with blood vessels.
In between pericardium and endothelium there are cardiac muscles. Connective tissue skeleton of heart separates chambers of heart. The vales of heart are of collagen.
The cardiac muscles structurally differ of striated and smooth muscles.
Muscle fibers of heart are branched and are interconnected.