Heart Chambers: Right and Left Atria and Ventricles in Step-by-Step Detail

This chapter focuses on what you see inside each chamber and how those structures support one-way blood flow. We will move in blood-flow order: right atrium → right ventricle → left atrium → left ventricle. For each chamber, use the same checklist: location → openings → internal landmarks → clinical relevance of structure.

Right Atrium (RA)

1) Location (where it sits and what it faces)

The right atrium forms the right-sided receiving chamber of the heart. It lies superior to the right ventricle and acts as the entry hall for systemic venous blood returning to the heart.

2) Openings (inflow and outflow)

• Inflow: superior vena cava (SVC) and inferior vena cava (IVC) openings deliver deoxygenated blood.
• Additional inflow: coronary sinus opening returns venous blood from the myocardium.
• Outflow: right atrioventricular (AV) orifice leads to the tricuspid valve and into the right ventricle.

3) Internal landmarks (what you should identify)

• Pectinate muscles: ridged muscular bands, most prominent in the right atrial appendage and anterior wall. They increase contractile efficiency without greatly increasing mass.
• Crista terminalis: a muscular ridge separating the smooth posterior wall (sinus venarum) from the rough pectinate region.
• Fossa ovalis: an oval depression on the interatrial septum, the remnant of the fetal foramen ovale. The raised rim is the limbus.
• Smooth vs rough walls: posterior RA wall is smoother (receives SVC/IVC), while the anterior portion is more trabeculated by pectinate muscles.

4) Clinical relevance of structure (why it matters)

• Fossa ovalis: incomplete postnatal closure can leave a patent foramen ovale (PFO), which may allow intermittent right-to-left shunting under certain pressure conditions.
• Crista terminalis and pectinate region: important landmarks during electrophysiology procedures; atrial tissue architecture can influence conduction pathways.
• Coronary sinus opening: relevant for placing certain pacing leads and for understanding venous drainage of the heart.

Right Ventricle (RV)

1) Location (where it sits and what it faces)

The right ventricle is the main pumping chamber for pulmonary circulation. It sits inferior to the right atrium and wraps partly around the left ventricle. Functionally, it pumps blood a short distance to the lungs at relatively low pressure.

2) Openings (inflow and outflow)

• Inflow: right AV orifice through the tricuspid valve from the right atrium.
• Outflow: right ventricular outflow tract (infundibulum/conus arteriosus) leading to the pulmonary valve and pulmonary trunk.

3) Internal landmarks (what you should identify)

• Trabeculae carneae: irregular muscular ridges lining the ventricular wall; they help prevent suction during contraction and contribute to efficient ejection.
• Papillary muscles: muscular projections (commonly anterior, posterior, and septal groups) that attach to chordae tendineae, which tether tricuspid valve leaflets.
• Chordae tendineae: fibrous cords connecting valve leaflets to papillary muscles; they prevent valve prolapse into the atrium during systole.
• Ventricular septum (septal wall): shared wall between ventricles; its contour contributes to RV shape and function.
• Inflow vs outflow regions: the inflow portion is more trabeculated; the outflow tract is smoother to streamline blood toward the pulmonary valve.

4) Wall thickness characteristics and functional implications

The RV wall is thinner than the LV because it generates lower pressures for pulmonary circulation. A thinner wall is sufficient for moving blood through the low-resistance pulmonary vascular bed.

5) Clinical relevance of structure (why it matters)

• Papillary muscles + chordae: if papillary muscles are dysfunctional (e.g., ischemia) or chordae rupture, the tricuspid valve may not coapt properly, contributing to regurgitation.
• Trabeculae carneae: prominent trabeculations can be mistaken for masses on imaging; learning the normal pattern helps interpretation.
• Ventricular septum: defects in the septum (VSDs) allow abnormal shunting between ventricles; septal position can shift with pressure overload.

Left Atrium (LA)

1) Location (where it sits and what it faces)

The left atrium is the receiving chamber for oxygenated blood from the lungs. It sits superior to the left ventricle and functions as a reservoir and conduit into the left ventricle.

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2) Openings (inflow and outflow)

• Inflow: pulmonary veins (typically four) deliver oxygenated blood into the left atrium.
• Outflow: left AV orifice leads through the mitral (bicuspid) valve into the left ventricle.

3) Internal landmarks (what you should identify)

• Smoother interior: compared with the right atrium, the left atrium is generally smoother because it is largely formed by incorporation of pulmonary venous tissue.
• Pectinate muscles: present but mostly confined to the left atrial appendage; the main chamber walls are less ridged than in the RA.
• Interatrial septal area: the fossa ovalis is seen from the left side as a thinner region of the septum (the valve of the foramen ovale), rather than a prominent depression.

4) Wall thickness characteristics and functional implications

The LA wall is relatively thin, designed for receiving blood and assisting ventricular filling rather than generating high pressures. Its contraction provides an “atrial kick” that becomes more important when ventricular filling is impaired.

5) Clinical relevance of structure (why it matters)

• Left atrial appendage: because it is a small cul-de-sac with pectinate ridges, blood can stagnate there when atrial contraction is ineffective (e.g., atrial fibrillation), increasing clot risk.
• Mitral inflow: structural changes affecting mitral valve function alter LA pressure and can lead to LA enlargement over time.

Left Ventricle (LV)

1) Location (where it sits and what it faces)

The left ventricle is the main systemic pumping chamber. It sits inferior to the left atrium and generates the force needed to propel blood through the entire body.

2) Openings (inflow and outflow)

• Inflow: left AV orifice through the mitral valve from the left atrium.
• Outflow: left ventricular outflow tract leading to the aortic valve and into the aorta.

3) Internal landmarks (what you should identify)

• Trabeculae carneae: present but typically finer and more uniform than in the RV; they line the ventricular wall.
• Papillary muscles: usually two major papillary muscles (anterolateral and posteromedial) that anchor chordae tendineae to the mitral valve leaflets.
• Chordae tendineae: prevent mitral valve prolapse during systole by tethering leaflets to papillary muscles.
• Ventricular septum: forms the medial wall of the LV; the septum is thick and contributes significantly to LV contractile power.
• Smoother outflow tract: the region leading to the aortic valve is smoother to facilitate efficient ejection.

4) Wall thickness characteristics and functional implications

The LV wall is the thickest because it must generate high pressure to overcome systemic vascular resistance. Greater muscle mass supports stronger contractions and higher systolic pressures.

5) Clinical relevance of structure (why it matters)

• Papillary muscles + chordae: papillary muscle ischemia or chordal rupture can cause acute mitral regurgitation, rapidly increasing LA pressure and pulmonary congestion.
• Ventricular septum: hypertrophy or scarring can affect outflow dynamics and conduction pathways; septal defects alter pressure/flow relationships between ventricles.
• Wall thickness: chronic pressure overload can lead to LV hypertrophy, changing chamber compliance and filling.

Quick Comparison Table (use for self-check)

Internal Heart “Tour” Activity (label + narrate)

Part A: Label a cross-sectional diagram

Use a simple cross-sectional heart diagram (four chambers visible). Label the following structures. Work chamber-by-chamber in blood-flow order.

• Right atrium: SVC opening, IVC opening, coronary sinus opening, tricuspid valve (right AV orifice), pectinate muscles, crista terminalis, fossa ovalis (on septum).
• Right ventricle: trabeculae carneae, papillary muscles, chordae tendineae, interventricular septum (ventricular septum), pulmonary valve/outflow tract.
• Left atrium: pulmonary vein openings, mitral valve (left AV orifice), left atrial appendage region (pectinate muscles concentrated here).
• Left ventricle: trabeculae carneae, papillary muscles, chordae tendineae, interventricular septum, aortic valve/outflow tract.

Part B: Narrate the blood path (step-by-step script)

Read your labels and narrate out loud. Keep your finger on the diagram as you speak.

1. Step 1 (RA filling): “Blood enters the right atrium through the SVC, IVC, and coronary sinus. I can see the pectinate muscles and the fossa ovalis on the septum.”

2. Step 2 (RA → RV): “Blood passes through the tricuspid valve into the right ventricle.”

3. Step 3 (RV ejection): “Inside the RV, the trabeculae carneae line the wall, and papillary muscles with chordae tendineae stabilize the valve during contraction. Blood exits through the pulmonary valve.”

4. Step 4 (LA filling): “After the lungs, blood returns to the left atrium through the pulmonary veins. The chamber is smoother, with pectinate muscles mainly in the appendage.”

5. Step 5 (LA → LV): “Blood flows through the mitral valve into the left ventricle.”

6. Step 6 (LV ejection): “The LV has the thickest wall. The papillary muscles and chordae tendineae prevent mitral prolapse, and blood leaves through the aortic valve. The ventricular septum forms the shared wall between ventricles.”

Self-check prompts (use after your narration)

• Did you name one inflow and one outflow for each chamber?
• Did you point to pectinate muscles (RA and LA appendage) and trabeculae carneae (ventricles) correctly?
• Did you identify the fossa ovalis on the interatrial septum and the ventricular septum between ventricles?
• Did you explain why the LV wall is thicker than the RV wall?