Cardiac Anatomy

Overview
  • The heart sits within the mediastinum and inside the pericardium. It is situated slightly askew with roughly a third of the organ to the left of the medial plane.
Basic Architecture
  • The heart is composed of four chambers of two basic functional types, atria and ventricles. Atria receive blood from the vasculature and discharge into ventricles, while ventricles receive blood from atria and discharge into the vasculature. Although fused together, the heart can be thought of as two separate pumps, the right heart and the left heart, each of which is composed of an atrium and a ventricle. The heart actuates movement of blood purely by changing the volume of these chambers which on its own cannot provide directional flow of blood. Directionality of blood flow is provided by four one-way cardiac valves which are positioned at the outlet of these chambers, thus allowing entry and exit of blood only in a specified direction.
Anatomical Reference Points
  • Surfaces
    • Anterior Surface: Is formed mostly by the right ventricle
    • Inferior Surface: Which sits on top of the diaphragm is formed mostly by the left ventricle and a little of the right ventricle
    • Left Surface: Formed mainly by the left ventricle
    • Right Surface: Formed mainly by the right ventricle
  • Borders
    • Right Border: Formed by the right atrium
    • Left Border: Formed mainly by the left ventricle
    • Inferior Border: Formed mainly by the right ventricle and a small segment of the left ventricle
    • Superior Border: Formed by the left and right atria and is the location from which the great vessels arise
  • Apex and Base
    • Cardiac Apex: Refers to the conical, left terminus of the heart which is composed mostly of the left ventricle. The apex sits deep to the 5th Intercostal Space about 9cm to the left of the medial plane and the heart's beating can be best felt at this location
    • Cardiac Base: Refers to the posterior aspect of the heart which is mainly formed by the left atrium and part of the right atrium. The cardiac base sits on top of the vertebrae, esophagus, and aorta
Chambers
  • Right Atrium
    • The right atrium receives deoxygenated systemic blood from the superior vena cava, inferior vena cava, and the coronary sinus. The right atrium outlets blood through the tricuspid valve into the right ventricle. The interatrial septum possesses an oval shaped depression termed the "Fossa Ovalis" which is a remnant of the embryonic Foramen Ovale.
  • Right Ventricle
    • Blood received from the atrium through the tricuspid valve enters the right ventricle. The right ventricle outlets blood into the pulmonary artery and thus into the pulmonary circulation via the pulmonic valve. The interventricular septum separates the right from the left ventricle.
  • Left Atrium
    • The Left Atrium receives oxygenated pulmonary blood from four, symmetrically arranged pulmonary veins which open into the atrium at the posterior aspect of the heart. The Left Atrium outlets blood through the mitral valve into the left ventricle.
  • Left Ventricle
    • The Left Ventricle is the largest, most muscular chamber of the heart and is responsible for pumping blood through the systemic circulation. It receives oxygenated blood via the mitral valve from the left atrium and pumps the blood through the aortic valve into aorta and thus the systemic circulation.
Heart Valves
  • Overview
    • The cardiac valves are tough, yet thin and flexible cusps which open to let blood flow in the anterograde direction but close tightly against one another to prevent blood flow in the retrograde direction. The valves are attached to a very tough, fibrous skeleton which forms the annular border of the valvular orfices through which blood flows. Interestingly, all of the valves exist within a single cardiac fibrous skeleton which roughly forms a plane with four holes representing the four orifices. The tricuspid valve and mitral valve are architecturally similar and are thus referred to as Atrioventricular Valves (AV Valves). The pulmonic and aortic valves are also architecturally similar and are thus referred to as the semilunar valves. Because atrioventricular orifices are large in diameter, their cusps require some architectural support to prevent inversion during ventricular systole. This architectural support is provided by the chordae tendineae and papillary muscles described below.
  • Tricuspid Valve
    • The Tricuspid Valve separates the Right Atrium from the Right Ventricle and is composed of three cusps from which the valve derives its namesake. The free edges of these cusps are attached to fine tendinous chords (Chordae Tendineae) which in turn are attached to tubular papillary muscles that emerge from the right ventriclular inner surface. The Chordae Tenineae and the Papillary Muscles together prevent the cusps from inverting during ventricular systole and thus allowing retrograde blood flow.
  • Pulmonic Valve
    • The pulmonic valve separates the right ventricle from the pulmonary artery and is composed of three cusps.
  • Mitral Valve
    • The mitral valve separates the left atrium from the left ventricle and is composed of only two cusps. Like the tricuspid valve, chordae tendineae and papillary muscles are attached to the free edges of the mitral cusps and help ensure that the cusps do not invert during the powerful left ventricular systole.
  • Aortic Valve
    • The aortic valve separates the left ventricle from the aorta and is composed of three cusps much like the pulmonic valve
Coronary Arteries
  • Overview
    • The coronary arteries are the first branches of the aorta and provide the arterial blood supply for the heart. Because proper blood flow through the coronary arteries is critical for functioning of the heart, stenosis or occlusion of these arteries during processes of Ischemic Heart Disease results in the dramatic clinical consequences. Familiarity with the anatomical distribution of the coronary arteries is important for assessing what areas of the myocardium will be affected when particular segments of these vessels become occluded or stenosed. Two basic coronary arteries exist, the Right and Left Coronary Arteries, which branch off of the Aorta directly above the aortic valves within small dilations of the aorta known as the aortic sinuses. Although there is substantial individual variation in the distribution of the coronary arteries, the central themes are described below.
  • Right Coronary Artery (RCA)
    • The RCA branches off of the right aortic sinus and travels down the groove which defines the anterior border between the right atrium and right ventricle. It then continues around the inferior border of the heart to the cardiac posterior surface where it travels down the groove which defines the posterior border between the right and left ventricles. During its course it sends off branches which supply the AV Node, most of the right atrium and right ventricle, along with the posterior third of the interventricular septum. In roughly half of individuals, the SA Node is also supplied by a branch from the RCA.
  • Left Coronary Artery (LCA)
    • The LCA arises from the left aortic sinus and travels a brief distance down the groove which defines the border between the left atrium and left ventricle. It then branches into an anterior interventricular branch which runs down the anterior groove between the right and left ventricles, supplying the anterior two thirds of the interventricular septum. The other branch is known as the Left Circumflex Artery (LCx) which continues through the left atrio-ventricular groove around the left border of the heart to its posterior where in about half of individuals it supplies the SA Node. Large branches from both the left interventricular artery and the left circumflex separate to supply the majority of the left ventricle. In total, the LCA supplies the anterior two-thirds of the interventricular septum, the left atrium, most of the left ventricle.