The heart is a thick muscular organ with four cavitated parts located in the middle part of the inferior mediastinum, known as the middle mediastinum. It is a central organ and pump of the cardiovascular system that maintains the unidirectional flow of blood through the circulatory system.

External anatomy

The heart consists of the right and left side (or right and left pump) and four main parts: right atrium and right ventricle, left atrium and left ventricle. The heart is surrounded by a serous sac called the pericardium. The great vessels originating from the heart provide blood flow throughout the whole body.

The heart has a cone or pyramid shape with the base projected upward, backward, and to the right, while the apex projects forward, downward, and to the left.  Approximately two-thirds of the heart is located on the left, while one-third on the right side from the midline of the body. The apex of the heart is typically located deep to the left 5th intercostal space and is formed by the left ventricle.

Besides the apex and base, the heart has four more surfaces formed by different internal parts. Also, four borders of the heart can be distinguished:

• Superior border - formed by the right and left atria, auricles, and the great vessels;
• Right border - formed by the right atrium extending between the superior and inferior vena cavae;
• Left border - created by the left ventricle and left auricle;
• Inferior border - formed by the left and right ventricles.

Also, the outer surfaces of the heart contain grooves - external sulci, which are created by the internal partitions of the organ. 

Neurovascular supply

The heart receives its arterial blood supply from the left and right coronary arteries and their branches. The venous blood from the heart is collected by the coronary sinus and its tributary veins.

The innervation of the heart comes from the autonomic nervous system via the cardiac plexus that contains both parasympathetic and sympathetic fibers. The parasympathetic fibers are provided by the vagus nerve (CN X). The sympathetic fibers of the cardiac plexus arise from the lower cervical and upper thoracic ganglia of the sympathetic trunk.