Pericardium, Myocardium and Endocardium The heart is protected by the ribcage in the chest cavity. It is enclosed in a sack that provides increased protection. This sack, or pericardium, is a fluid-filled, (although the space is very small, so the volume of fluid is very low) membranous structure that separates the heart from the lungs within the chest. It is made up of the visceral pericardium, which is actually the outer epicardial layer of the heart, and the parietal pericardium. At times, the pericardium can become inflamed, which is a condition called pericarditis. The heart is made of three layers, the endocardium, the myocardium, and the epicardium. Theendocardium is the innermost layer of the heart that forms a barrier between the muscle layers of the heart and blood. The myocardium is the thickest of the three layers of heart tissue. It is the cardiac muscle layer that contracts and generates force to pump the blood. The outermost layer of the heart is theepicardium. It is a thin layer of cells that covers the outside of the heart and forms the visceral layer of the pericardium. The epicardium protects the heart within the thorax. Diseases of the Heart: Cardiac Tamponade Inflammation of the pericardium can result in cardiac tamponade. When the pericardium gets infected fluids or blood can accumulate between the layers of the pericardium. This increases the pressure that is exerted on the outside of the heart and prevents the heart from filling appropriately during diastole. If the heart does not fill normally, the stroke volume decreases. The body can try to compensate with an increased heart rate and force of contraction (both effects of the sympathetic nervous system), but if this is not enough, the person will go into heart failure. .