Anatomy of the Heart

Anatomy of the Heart

• The heart is a four-chambered muscular pump
• It consists of the right atrium, left atrium, right ventricle, and left ventricle
• Both atria receive venous (deoxygenated) blood
• The right ventricle pumps blood to the lungs
• The left ventricle pumps blood to the systemic circulation

Heart - Anterior View

• Structures include the brachiocephalic artery, right brachiocephalic vein, azygos vein, right pulmonary artery, left common carotid artery, left brachiocephalic vein, left subclavian artery, ligamentum arteriosum, left pulmonary artery, pulmonary veins, right atrium, inferior vena cava, right ventricle, ascending aorta, and apex.

Heart - Posterior View

• Structures include brachiocephalic artery, right brachiocephalic vein, azygos vein, right pulmonary artery, left common carotid artery, left brachiocephalic vein, left subclavian artery, ligamentum arteriosum, left pulmonary artery, pulmonary veins, right atrium, inferior vena cava, right ventricle, left ventricle, and apex.

Position and Borders

• The heart is positioned obliquely in the thoracic cavity
• The right border is primarily the right atrium
• The inferior border is mainly the right ventricle and a portion of the left ventricle
• The apex is located at the junction of the inferior and left borders
• The left border is primarily the left ventricle
• The anterior surface is mostly the right ventricle (RV) with the right atrium (RA) on the right side
• The posterior surface is the base and is formed by the left atrium (LA) and the four pulmonary veins.

Right Atrium

• It's an elongated chamber between the superior vena cava (SVC) and inferior vena cava (IVC)
• Forms the right border of the heart
• The lower end is formed by the IVC orifice
• The upper end is extended as the right auricle, overlying the aorta
• The myocardium contains pectinate muscles (horizontal ridges)
• The interatrial septum forms the posterior wall of the RA
• It includes the fossa ovalis (shallow depression)
• The coronary sinus opens into the RA

Right Ventricle

• Projects to the left of the right atrium
• Separated from the RA by the atrioventricular groove, which contains the right coronary artery
• Its walls have trabeculae carneae (muscular ridges)
• Papillary muscles connect the ventricular wall to the tricuspid valve cusps

The Tricuspid Valve

• Guards the right atrioventricular opening
• It has three cusps: anterior, posterior, and septal
• Cusps are attached to papillary muscles by chordae tendineae (collagenous cords), preventing eversion during ventricular contraction

The Pulmonary Valve

• Separates the pulmonary conus from the pulmonary trunk
• It has three semilunar cusps

The Left Atrium

• Forms the posterior surface of the heart, posterior to the right atrium
• Smooth-walled cavity, except for the auricle, which has musculi pectinati (muscular ridges)
• Four pulmonary veins enter the LA symmetrically and are valveless

The Mitral Valve

• A bicuspid valve (2 cusps) allowing blood flow from the left atrium (LA) to the left ventricle (LV) during diastole
• Named anterior and posterior

The Left Ventricle

• Forms the apex of the heart, its walls are thicker than those of the right ventricle
• Well-developed trabeculae carneae
• Two papillary muscles (anterior and posterior), each connected to chordae tendineae

The Aortic Valve

• Guards the aortic orifice at the entrance to the ascending aorta
• Has three semilunar cusps (right, left, and posterior)
• Closes during ventricular diastole, contributing to the second heart sound (S2)
• Prevents backflow of blood into the left ventricle

The Ascending Aorta

• Immediately above the aortic orifice, the ascending aorta bulges to form the aortic sinuses of Valsalva
• Three aortic sinuses (left, right, and posterior)
• The left sinus gives rise to the left coronary artery, and the right sinus to the right coronary artery. No vessels arise from the posterior sinus (called the non-coronary sinus)

The Conducting System

• Consists of the sinoatrial node (SAN), atrioventricular node (AVN), atrioventricular bundle (of His), right and left bundle branches, and Purkinje fibers
• SAN is the cardiac pacemaker, located subepicardially in the right atrium (just below the SVC)
• AVN is a specialized mass of myocardial cells in the right atrium
• The bundle of His runs in the interventricular septum
• Divides into right and left bundle branches
• These branches are the only conduction pathway from the atria to the ventricles, separated by fibrous tissues