Please correct any grammer in the following.
The heart is one of the most important organs of the body. The structure and organization can be of interest. The heart about the size of a fist is located between the two lungs of the thoracic cavity. The membrane that surrounds and protects the heart is the pericardium. This consist of two parts; the fibrous (outer) and the serous (inner) pericardium. The fibrous provides protection and holds the heart in place, while the serous provides a double layer around the heart. The outer layer of the inner pericardium is fused to the outer while the inner layer is secured tightly around the surface of the heart.
The heart wall is composed of three layers; the epicardium (external), myocardium (middle) and the endocardium (inner). The epicardium is the thin and transparent outer layer of the wall. It is also composed of two tissues; the mesothelium and connective tissues. The myocardium consist of the cardiac muscle tissue while the endocardium is a thin layer of simple squamas epthium that lines the inside of the myocardium and covers the valves of the heart and the tendons that are attached.
The heart contains four chambers; two upper (atria) and two lower (ventricles). The two atriums are separated by a thin partition; the interation septum. Within the atria, the right atrium receives deoxygenated blood from three veins; the superior vena cava, inferior vena cava and the coronary sinus. With the ventricles, the left one pumps blood only into the lungs while the right one pumps to all other parts of the body.