Some facts:

The heart is a cone-shaped muscular organ, weighing roughly 9-12 oz (255-340 g.) and measuring 5″ (12,5 cm) long and 3 1/2″ (9cm) wide, located in the mediastinal cavity (mediastinum). The top of the heart is the base, the bottom of the heart is the apex, tilting forward and down, toward the left. The heart rests on the diaphragm.

Structure

The heart consists of four chambers, two atria and two ventricles. The right part of the heart receives blood to the right atrium via the superior and the inferior venae cavae. Blood from the right atrium goes into the right ventricle, through the tricuspid valve. The right ventricle pumps blood through the pulmonic valve into the pulmonary arteries and, eventually, into the lungs. From the lungs, the blood flows through the pulmonary veins and into the left atrium. From the left atrium, blood passes through the mitral valve, into the left ventricle and from the left ventricle into the aorta.

Left and right atria are separated by the interatrial septum; left and right ventricles are separated by the interventricular septum.

Valves

The heart contains four valves:
Atrio-ventricular valves:
left atrium –> left ventricle : mitral valve (two cups)
right atrium –> right ventricle : tricuspid valve (three cups)

Semilunar valves:
left ventricle –> aorta : aortic valve
right ventricle –> pulmonary trunk : pulmonary valve

When closed, the valves form a tight seal, preventing regurgitation of the blood.

Structure

The heart’s wall consists of the pericardium, the epicardium, the myocardium and the endocardium.

a) pericardium
A thin, fibrous sac, composed of tough fibrous tissue, in which the heart is enclosed.
The pericardium consists of the serous pericardium and the fibrous pericardium.
The serous pericardium, the inner portion, has two layers: the parietal layer and the visceral layer (which adheres to the surface of the heart, the epicardium).
The fibrous pericardium attaches to the diaphragm, sternum and the great vessels.
The pericardial space, the space between the parietal and the visceral layer, contains the pericardial fluid, which lubricates the two surfaces and cushions theheart.

b) epicardium
The outer layer of the heart and the visceral layer of the serous pericardium.

c) myocardium
Muscle tissue of the heart, generating the force of the contraction. The myocardium consists of muscle cells, the cardiac myocytes, connected together by intercalated discs.

d) endocardium
Endothelial tissue that covers the inside of the heart and the valves.

Coronary circulation

The coronary arteries (left and right) supply the heart with oxygenated blood. Blood passes to the coronary arteries through the coronary ostium, which is located near the aortic valve.
From the right coronary artery originate the posterior descending and the right marginal branches.
The left coronary artery divides into the circumflex, the left marginal and the anterior descending branches.
The blood returns to the right atrium via the coronary sinus.