Learning Objective

Understand the anatomical structure, embryological origins, and clinical significance of the atria and ventricles, their inflow and outflow portions, valves, septa, and the pathophysiology of common congenital defects such as atrial septal defect and Tetralogy of Fallot.

Chambers of the Heart

The heart consists of four chambers – two atria and two ventricles:

Blood returning to the heart enters the atria, then is pumped into the ventricles.
From the left ventricle, blood passes into the aorta and enters the systemic circulation.
From the right ventricle, blood enters the pulmonary circulation via the pulmonary arteries.

In this article, we shall look at the anatomy of the chambers of the heart – their location, internal structure, and clinical correlations.

Atria

Right Atrium

The right atrium receives deoxygenated blood from the superior and inferior vena cavae and coronary veins. It pumps this blood through the right atrioventricular orifice (guarded by the tricuspid valve) into the right ventricle.

The right auricle is a muscular pouch extending from the antero-medial portion to increase atrial capacity. The interior surface of the right atrium has two parts separated by the crista terminalis:

Sinus venarum – posterior, smooth-walled, derived from the embryonic sinus venosus.
Atrium proper – anterior, includes the right auricle, lined by pectinate muscles, derived from the primitive atrium.

The coronary sinus opens into the right atrium between the inferior vena cava orifice and the right atrioventricular orifice.

Activity

Interatrial Septum

The interatrial septum separates the right and left atria. A small depression, the fossa ovalis, is the remnant of the foramen ovale in the fetal heart.

Clinical Relevance

Atrial Septal Defect: Persistent opening in the interatrial septum, commonly at the foramen ovale (patent foramen ovale), causing left-to-right shunting, right ventricular overload, pulmonary hypertension, and possible right heart failure. Treatment: surgical or transcatheter closure.

Left Atrium

Receives oxygenated blood from the four pulmonary veins and pumps it through the mitral valve into the left ventricle.

The interior has two parts:

Inflow portion – from pulmonary veins, smooth-walled.
Outflow portion – includes the left auricle, lined by pectinate muscles.

Activity

Ventricles

Right Ventricle

Receives blood from the right atrium and pumps it through the pulmonary valve into the pulmonary artery. It has inflow and outflow portions, separated by the supraventricular crest.

Inflow Portion

Trabeculae carneae – muscular elevations.
Ridges, Bridges (including moderator band), Papillary muscles attached via chordae tendineae to the tricuspid valve.

Outflow Portion (Conus arteriosus)

Derived from the embryonic bulbus cordis, smooth-walled, leading to the pulmonary artery.

Interventricular Septum

Separates the ventricles: the superior membranous and the inferior muscular parts.

Left Ventricle

Receives blood from the left atrium and pumps it through the aortic valve into the aorta. The inflow portion is lined by trabeculae carneae and two papillary muscles; the outflow portion is the aortic vestibule.

Activity

Clinical Relevance

Tetralogy of Fallot: Congenital cyanotic heart disease, including VSD, overriding aorta, pulmonary stenosis, and right ventricular hypertrophy. Surgical correction is required early in life.