Learning Objective

By the end of this lesson, you should be able to describe the orientation of the heart in the mediastinum. Identify its five surfaces and four borders, recognise the major sulci and their contents, and explain the clinical significance of the transverse pericardial sinus.

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Overview

The heart is a hollow muscular pump located in the middle mediastinum. It has a complex pyramidal shape, often described as
“a pyramid that has fallen over.”

The apex points anteroinferiorly and to the left. Externally, the heart is marked by grooves called sulci, which correspond to internal chamber divisions.

 

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Activity

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Orientation and Surfaces of the Heart

In anatomical position, the heart has five surfaces.

Surface	Formed Mainly By	Key Point
Anterior (Sternocostal)	Right ventricle	RV forms most of the anterior surface
Posterior (Base)	Left atrium	LA forms the base of the heart
Inferior (Diaphragmatic)	Left and right ventricles	Rests on the diaphragm
Right Pulmonary	Right atrium	Faces the right lung
Left Pulmonary	Left ventricle	Faces left lung

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Borders of the Heart

The surfaces are separated by four main borders.

Border	Formed By
Right Border	Right atrium
Inferior Border	Right and left ventricles
Left Border	Left ventricle (and part of left atrium)
Superior Border	Right and left atria + great vessels

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Activity

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Sulci of the Heart

The heart chambers create external grooves known as sulci.

1. Coronary Sulcus (Atrioventricular Groove)

• Separates atria from ventricles
• Contains:
  • Right coronary artery
  • Circumflex branch of the left coronary artery
  • Small cardiac vein
  • Coronary sinus

2. Anterior Interventricular Sulcus

• Separates left and right ventricles (anteriorly)
• Contains:
  • Left anterior descending (LAD) artery
  • Great cardiac vein

3. Posterior Interventricular Sulcus

• Separates ventricles (posteriorly)
• Contains:
  • Posterior interventricular artery
  • Middle cardiac vein

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Activity

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Pericardial Sinuses

Pericardial sinuses are passageways formed by the folding of the pericardium around the great vessels.

Oblique Pericardial Sinus

• Blind-ending recess
• Located posterior to the left atrium

Transverse Pericardial Sinus

• Posterior to the ascending aorta and the pulmonary trunk
• Anterior to superior vena cava
• Superior to the left atrium

It separates:

• Arterial outflow (aorta, pulmonary trunk)
• Venous inflow (SVC, pulmonary veins)

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Clinical Relevance

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Transverse Pericardial Sinus in CABG

During coronary artery bypass grafting (CABG), surgeons pass a clamp through the transverse pericardial sinus
to ligate the aorta and pulmonary trunk. This is a high-yield surgical anatomy landmark.

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Activity