The mitral valve, also known as the bicuspid valve, has two cusps (anterior and posterior) attached to papillary muscles by cordae tendineae, preventing backflow into the left atrium. The pulmonary and aortic semilunar valves, each with three cusps, allow blood flow out of the ventricles but prevent backflow during ventricular relaxation. These valves lack cordae tendineae; instead, their cusps catch reverse blood flow and snap shut. Dilations above the semilunar cusps form sinuses, which also house the origins of the coronary arteries.

The heart, a muscular organ slightly larger than a clenched fist, is situated in the thorax, specifically in the mediastinum between the lungs. Enclosed by the pericardium, its primary role is to pump oxygen-rich blood to the body and send deoxygenated blood to the lungs for gas exchange. The heart consists of four chambers: the right atrium and ventricle forming the right heart, and the left atrium and ventricle forming the left heart.

Deoxygenated blood enters the right atrium via the superior and inferior vena cava, then flows into the right ventricle, which pumps it to the lungs through the pulmonary trunk (pulmonary circulation). Oxygenated blood returns from the lungs through four pulmonary veins, draining into the left atrium. From there, it moves into the left ventricle and is pumped into the aorta, distributing to the entire body (systemic circulation).

The heart is shaped like an upside-down, tipped-over pyramid with a posterior base and an apex pointing anteriorly and slightly left. In a two-dimensional view, it resembles a trapezoid with superior, inferior, right, and left borders. The superior border is formed by the Atria, the inferior by the right and left ventricles, the right by the right atrium, and the left primarily by the left ventricle. These borders, visible on chest x-rays, indicate the heart's rotation within the mediastinum.

The anterior view reveals the four chambers and great vessels, including the right atrium and ventricle, separated by the coronary sulcus, and the left atrium's auricle and left ventricle, also separated by the coronary sulcus. The ventricles are divided by the anterior interventricular sulcus. Key great vessels visible include the superior and inferior vena cava, ascending aorta, aortic arch branches, and pulmonary trunk. The posterior view shows the left atrium, left auricle, most of the posterior left ventricle, right atrium, and right ventricle, separated by the coronary sulcus and posterior interventricular sulcus. Pulmonary veins and arteries, the aortic arch, and superior and inferior vena cava are also prominent. The right ventricle is the most anterior part, and the left atrium is the most posterior.

The right atrium has a smooth posterior part (sinus venarum) where the superior and inferior vena cava and coronary sinus open, and a rough anterior part with pectinate muscles. These parts are separated externally by the sulcus terminalis and internally by the crista terminalis. Blood flows from the right atrium through the right AV (tricuspid) orifice into the right ventricle. The right and left atria are divided by the interatrial septum, which features the fosa ovalis, a remnant of the fetal foramen ovale.

The right ventricle has an inflow part with muscular elevations (trabeculae carneae) and an outflow part (conus arteriosus) leading to the pulmonary trunk. Blood enters through the tricuspid orifice, guarded by the tricuspid valve with three cusps (anterior, posterior, septal) anchored by cordae tendineae to papillary muscles. This mechanism prevents backflow into the right atrium during systole. The interventricular septum separates the ventricles, comprising muscular and membranous parts.

During contraction of the right atrium, blood flows into the right ventricle through the tricuspid valve. Subsequently, blood exits the right ventricle via the pulmonary valve into the pulmonary trunk, heading to the lungs for oxygenation.

The left atrium is thicker than the right and, along with the left auricle, forms a large part of the heart's base. The four pulmonary veins enter its smooth posterior part. The interatrial septum features a semilunar depression, the valve of the oval fossa. Blood flows from the left atrium into the left ventricle via the left AV (mitral) orifice. The left ventricle forms the heart's apex and has thicker walls than the right due to higher pressure. It contains finer trabeculae carneae and a smooth aortic vestibule leading to the aortic orifice and aortic valve.

The heart contains a conducting system including the sinoatrial (SA) node, the heart's pacemaker, located at the junction of the superior vena cava and right atrium. Impulses from the SA node cause atrial contraction and then spread to the atrioventricular (AV) node (located in the interatrial septum). The AV node then transmits impulses via the AV bundle, which branches into right and left bundles that further stimulate the ventricles through Purkinje fibers, ensuring coordinated ventricular contraction.

The heart is innervated by the cardiac plexus, located anterior to the tracheal bifurcation. This plexus contains sympathetic fibers (increasing heart rate, force of contraction, and coronary blood flow) and parasympathetic fibers (slowing heart rate), as well as visceral afferent fibers for reflexes and pain sensation. These fibers ensure the heart adjusts to the body's demands.