The heart is made up of three layers: the epicardium, the myocardium, and the endocardium.
The epicardium is the outermost layer of the heart and is made up of epithelial cells and connective tissue. It is part of the visceral pericardium, the innermost portion of the pericardial sac, an empty sac with a tiny amount of lubricating fluid in it which surrounds the heart. The outer most portion of the pericardial sac is the parietal pericardium.
This blood enters the thin-walled right atrium, the first area of the right side of the heart to receive blood. With atrial contraction the blood is pumped through the open tricuspid valve (an atrioventricular valve) into the right ventricle, which has thicker walls than the atrium. The tricuspid valve then closes.
Heart Murmurs can be functional (innocent) or organic and are caused by turbulence of flow in the heart or blood vessels, which causes vibrations of the heart or vessel walls, perceived as murmurs by the examiner. The louder the murmur, the more likely it is to be pathologic. Functional, benign, or innocent murmurs are usually soft (grade I or II) and usually occur in systole.