1.1 Chambers and Valves of the heart

Surface of the heart and the corresponding chambers

• The Heart has 5 anatomical surfaces, each formed by different chambers.

  1. Anterior surface (sternocostal):

     • Mainly formed by the right ventricle (RV)

     • Minor contribution from the right atrium (RA) and left ventricle (LV)

     • Clinical relevance: Most prone to traumatic injury; best visualised in anterior chest X-rays

  2. Right pulmonary surface:

     • Formed primarily by the right atrium (RA)

     • Lies adjacent to the right lung and pericardium

     • Important in transesophageal echocardiogram

  3. Left pulpmonary surface:

     • Formed primarily by the left ventricle (LV)

     • Contacts the left lung, helps to distinguish left heart border on the chest radiographs

  4. Interior pulmonary surface:

     • Formed by the right ventricles (RV) and left ventricles (LV)

     • Rests on the central tendon of the diaphragm

     • Clinical relevance: infarcts in this area may result from occlusion of the posterior descending artery (usually from RCA)

  5. Posterior surface (base of the heart):

     • Formed mainly by the left atrium (LA)

     • Minor contribution from the right atrium (RA)

     • Related to the esophagus and thoracic aorta

     • Clinical relevance: left atrial enlargement can compress the esophagus, affecting swallowing.

Borders of the Heart and chambers that define them

1. Right border

   • Formed by: Right atrium

   • Clinical importance: Shifts in this border may indicate atrial enlargement.

2. Inferior border

   • Formed by: Right ventricle and apex of the Left ventricle

   • Lies adjacent to the diaphragm; closely follows the central tendon in imaging

3. Left border

   • Formed by: Left ventricle and left auricle

   • Represents the lateral margin of the heart on imaging

4. Superior border

   • Formed by: Both atria (especially Left Atrium and auricle), infundibulum

   • Houses the origins of great vessels (aorta, pulmonary trunk, superior vena cava).

Cardiac skeleton, chambers and valves

Fibrous skeleton of the heart (cardiac skeleton)

• Definition: The fibrous skeleton is a dense connective tissue framework embedded in the myocardium. It serves several essential roles

• Structural support:

  • Provides a rigid framework that anchors the valve cusps

  • Prevent overstretching of the valve openings during the cardiac cycle

• Electrical insulation:

  • Acts as an electrical barrier between atrial and ventricular muscle masses.

  • Ensures proper delay of impulses between atria and ventricles via the AV node

• Components:

  • Right fibrous ring: Encircles and supports the tricuspid valve

  • Left fibrous ring: Supports the mitral (bicuspid) valve

  • Fibrous coronets: Support aortic and pulmonary valves

  • Annuli fibrosi: Four interconnected fibrous rings surrounding each valve

Heart chambers (Structure and function)

Right atrium

• Structure:

  • Thin-walled chamber

  • Contains openings for superior vena cava, inferior vena cava, and coronary sinus

  • Includes the right auricle

• Function:

  • Receives deoxygenated blood from the body

  • Sends blood to the right ventricle via the tricuspid valve

Right ventricle

• Structure:

  • Forms most of the anterior surface of the heart

  • Contains trabeculae carneae, papillary muscles, and moderator band

• Function:

  • Pumps deoxygenated blood to the lungs through the pulmonary valve into the pulmonary trunk

Left atriums

• Structure:

  • Forms most of the posterior (base) surface

  • Receives four pulmonary veins

  • Has a small left auricle

• Function:

  • Receives oxygenated blood from the lungs

  • Pumps it into the left ventricle via the mitral valve

Left venticle

• Structure:

  • Thickest myocardium of all chambers

  • Contains prominent trabeculae carneae and papillary muscles

• Function:

  • Pumps oxygenated blood into the aorta via the aortic valve

  • Supplies the entire systemic circulation

Heart valves and associated structures

Atrioventricular (AV) valves

• Tricuspid valve:

  • Located between right atrium and right ventricle

  • Has three cusps

• Mitral (Bicuspid) valve

  • Located between left atrium and left ventricle

  • Has two cusps

• Cordae tendineae:

  • Fibrous cords attached to valve cusps, preventing the prolapse of valve during ventricular contraction

• Papillary muscles:

  • Contract with ventricles

  • Pull on the cordae tendineae to maintain valve closure integrity

Semilunar valves

• Pulmonary valve:

  • Located between right ventricle and pulmonary trunk

  • Contains 3 cusps - does not give rise to coronary arteries

    • Right cusp

    • Left cusp

    • Anterior cusp

• Aortic valve:

  • Located between left ventricle and ascending aorta

  • Contains 3 cusps

    • Right coronary cusp — gives rise to the right coronary artery

    • Left coronary cusp — gives rise to the left coronary artery

    • Posterior (non-coronary) cusp — no coronary artery arises from the posterior cusp

• Common features of all semilunar cusps:

  • Nodule: Thickened central area at the free edge, helping in tight closure

  • Lunule: Thin crescent-shaped edge on either side of the nodule

  • Sinuses: Small pocket-like spaces behind each cusp that help prevent cusp adherence to the vessel wall and assist in closure during diastole