Endocardium, myocardium and epicardium, from inside out
Expansion
From inside out:
- Endocardium: endothelium on connective tissue, continuous with the vascular intima. Contains the Purkinje fibres in its subendocardial layer. Site of infective endocarditis and of mural thrombus
- Myocardium: cardiac muscle, thickest in the left ventricle. Site of infarction and myocarditis
- Epicardium (visceral pericardium): mesothelium over connective tissue containing the coronary vessels and fat
Beyond this lie the pericardial cavity, the parietal serous pericardium and the fibrous pericardium.
Cardiac skeleton: dense fibrous rings around the valve orifices, providing attachment and electrical insulation between atria and ventricles.
Valves are avascular folds of endocardium with a fibrosa core, nourished by diffusion, which is why they heal poorly and why vegetations form readily on damaged surfaces.
The layered structure explains the differing clinical pictures: pericarditis causes sharp pleuritic pain relieved by sitting forward with a friction rub, myocarditis causes heart failure and arrhythmia with raised troponin, and endocarditis causes murmurs, embolic phenomena and immune complex disease.