The human heart, despite its modest size and weight, is an organ of remarkable strength and endurance. Roughly the size of a fist, the heart weighs between 250 and 350 grams and is nestled within the mediastinum, the medial cavity of the thorax. It extends obliquely for about 12 to 14 cm, resting on the superior surface of the diaphragm. The heart is positioned anterior to the vertebral column and posterior to the sternum, with two-thirds of its mass lying to the left of the midsternal line. The lungs flank the heart laterally.

The heart's broad base points towards the right shoulder, while its apex points inferiorly towards the left hip. The apex can be felt as an apical impulse in the fifth intercostal space on the midclavicular line, which is an imaginary line that runs vertically down from the midpoint of the clavicle.

The heart is protected by a double-walled sac known as the pericardium. The fibrous pericardium, the superficial part of this sac, is a tough layer of dense connective tissue that protects the heart, anchors it to surrounding structures, and prevents it from overfilling with blood.

Beneath the fibrous pericardium lies the serous pericardium, a thin, slippery two-layer membrane that forms a closed sac around the heart. Its parietal layer lines the internal surface of the fibrous pericardium, attaching to the large arteries exiting the heart. The internal visceral layer, also known as the epicardium, is an integral part of the heart wall.

Between these layers is the pericardial cavity, containing a film of serous fluid that provides a friction-free environment for the heart. However, inflammation of the pericardium, or pericarditis, roughens these surfaces, potentially leading to adhesions of the visceral and parietal pericardium that impede heart activity. Severe cases may result in cardiac tamponade, a condition where excess inflammatory fluid compresses the heart and limits its ability to pump blood. This condition is treated by draining the excess fluid from the pericardial cavity and treating the underlying cause.