Learning Objectives

By the end of this section, the learner should be able to:

• Identify the anatomical orientation of the cardiac chambers
• Describe the surface anatomy of the heart
• Outline the layers and innervation of the pericardium
• Understand coronary artery supply and dominance patterns
• Apply anatomical knowledge to key clinical correlations

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Overview of Cardiac Anatomy

The heart is a muscular organ located in the middle mediastinum. It consists of four chambers:

• Right atrium (RA)
• Right ventricle (RV)
• Left atrium (LA)
• Left ventricle (LV)

Each chamber contributes differently to the external surfaces of the heart and has important clinical implications.

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Surface Anatomy and Chamber Orientation

Left Atrium (LA)

• Forms the most posterior part of the heart
• Lies directly anterior to the oesophagus

Clinical relevance:

Enlargement of the left atrium (e.g., in mitral stenosis) may cause:

• Compression of the oesophagus → dysphagia
• Compression of the left recurrent laryngeal nerve (branch of the vagus nerve)
  → hoarseness (Ortner syndrome)

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Right Ventricle (RV)

• Forms the most anterior surface of the heart
• Lies immediately behind the sternum

Clinical relevance:

• Most commonly injured chamber in blunt or penetrating chest trauma

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Inferior (Diaphragmatic) Surface

• Left ventricle: ~⅔ of the inferior surface
• Right ventricle: ~⅓ of the inferior surface

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Great Vessels and Adjacent Structures

Structures commonly related to the heart include:

• Superior vena cava (SVC)
• Inferior vena cava (IVC)
• Pulmonary artery
• Descending aorta
• Aortic knob
• Azygos vein

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Pericardium

• Layers of the Pericardium (Outer → Inner)
• Fibrous pericardium
• Parietal pericardium
• Epicardium (visceral pericardium)
• The pericardial space lies between the parietal pericardium and epicardium and normally contains a small amount of lubricating fluid.

Innervation

The pericardium is innervated by the phrenic nerve (C3–C5)

Clinical relevance:

Pericarditis can cause referred pain to the neck, shoulders, or arms (often left-sided)

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Layers of the Heart Wall

From superficial to deep:

• Epicardium
• Myocardium
• Endocardium

The myocardium forms the contractile component of the heart.

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Coronary Blood Supply

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Left Anterior Descending (LAD) Artery

Supplies:

• Anterior ⅔ of the interventricular septum
• Anterior surface of the left ventricle
• Anterolateral papillary muscle

Clinical note:

Most commonly occluded coronary artery

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Posterior Descending Artery (PDA)

Supplies:

• Posterior ⅓ of the interventricular septum
• Posterior ⅔ of the ventricular walls
• Posteromedial papillary muscle
• SA and AV nodes (depending on dominance)

Clinical relevance:

Infarction may cause bradycardia or heart block

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Right (Acute) Marginal Artery

Supplies the right ventricle

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Coronary Dominance

Coronary dominance is defined by the origin of the PDA:

Right-dominant circulation (most common):

• PDA arises from the RCA

Left-dominant circulation (~5–10%):

• PDA arises from the LCX

Codominant circulation (~10–20%):

• PDA arises from both RCA and LCX

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Coronary Blood Flow Timing

Blood flow to the left ventricle and interventricular septum peaks during early diastole

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Venous Drainage

• The coronary sinus runs in the left atrioventricular groove
• Drains venous blood from the myocardium into the right atrium