Heart lies in middle mediastinum, enclosed by pericardium.

Position

• ~1/3 right of median plane, ~2/3 left
• Rests on central tendon of diaphragm
• Between two lungs/pleural sacs

Shape and Size

Apex

• Formed entirely by left ventricle
• Direction: down, forward, left
• Surface marking: left 5th ICS, 9 cm from midsternal line; just medial to midclavicular line
• = apex beat / point of maximum impulse
• Children: may be 4th ICS, slightly more lateral

Base

• = posterior surface; mainly left atrium, partly right atrium
• Direction: backward + right
• Vertebral level: T5–T8 (lying); 1 level lower (erect)
• Receives: 4 pulmonary veins, SVC, IVC
• Posterior relations: oblique pericardial sinus, oesophagus, descending thoracic aorta, vertebral column
• LA enlargement → oesophageal compression (dysphagia), posterior indentation on barium swallow

Surfaces

LA not visible anteriorly — hidden by ascending aorta + pulmonary trunk

Borders

Sulci

Crux of heart = meeting of posterior IV sulcus + coronary sulcus + interatrial groove; AV nodal artery often arises near here

Relations in Mediastinum

Anterior (ant→post): sternum/costal cartilages → lung/pleura margins → pericardium → sternocostal surface (mainly RV)

Posterior: oblique sinus, oesophagus, descending thoracic aorta, vertebral column

Inferior: central tendon of diaphragm; liver/stomach below diaphragm

Lateral:

Surface Marking (4 points)

Valve Surface Marking

• All valves lie behind sternum, oblique line from left 3rd costal cartilage to right 6th costal cartilage

Auscultatory Areas (sound heard in direction of flow)

Mnemonic clockwise from upper right: A-P-T-M

Cardiac Shadow (PA CXR)

Right border: upper = SVC; lower = right atrium

Left border (top→bottom): aortic knuckle → pulmonary trunk/conus → left auricle → left ventricle

LA enlargement straightens/bulges left auricular segment; aortic knuckle prominent with age/HTN/atherosclerosis; RA enlargement increases right lower border

Superficial Cardiac Dullness

• Area not covered by lung (cardiac notch); overlies RV; percussion dullness
• Loss in: emphysema, left pneumothorax, lung hyperinflation

Heart Sounds

The heart lies in the middle mediastinum, enclosed by the pericardium. Its surfaces, borders, surface markings, and X-ray shadow are high-yield because they connect gross anatomy with clinical examination, auscultation, percussion, and chest radiology.

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Position

The heart lies obliquely behind the sternum and costal cartilages.

Key position facts:

• About one-third lies to the right of the median plane.
• About two-thirds lies to the left of the median plane.
• It rests on the central tendon of diaphragm.
• It is enclosed in the pericardium.
• It lies between the two lungs and pleural sacs.

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Shape and Size

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Apex

The apex is formed entirely by the left ventricle.

In young children, the apex may lie in the 4th intercostal space and slightly more lateral.

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Base

The base is the posterior surface of the heart.

Relations posterior to the base:

• Oblique pericardial sinus
• Oesophagus
• Descending thoracic aorta
• Vertebral column

Clinical importance:

• Enlargement of the left atrium may compress the oesophagus and produce dysphagia.
• Left atrial enlargement may produce a posterior indentation on barium swallow.

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Surfaces of the Heart

The left atrium is not visible on the anterior surface because it is hidden by the ascending aorta and pulmonary trunk.

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Borders of the Heart

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Sulci of the Heart

The crux of the heart is the meeting point of:

• Posterior interventricular sulcus
• Coronary sulcus
• Interatrial groove

It is important because the AV nodal artery often arises near this region.

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Relations of the Heart in the Mediastinum

Anterior Relations

From anterior to posterior:

1. Sternum and costal cartilages
2. Anterior margins of lungs and pleura
3. Pericardium
4. Sternocostal surface of heart

The anterior surface is formed mainly by the right ventricle.

Posterior Relations

The posterior surface / base is related to:

• Oblique sinus of pericardium
• Oesophagus
• Descending thoracic aorta
• Vertebral column

Inferior Relations

• Central tendon of diaphragm
• Left lobe of liver and stomach lie below the diaphragm

Lateral Relations

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Surface Marking of the Heart

The outline of the heart can be marked by four points.

Joining these points gives:

• Right border: nearly vertical
• Inferior border: nearly horizontal
• Left border: curved
• Upper border: oblique

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Surface Marking of Cardiac Valves

All valves lie behind the sternum along an oblique line from the left 3rd costal cartilage to the right 6th costal cartilage.

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Auscultatory Areas

Valve sounds are best heard in the direction of blood flow, not directly over the anatomical valve position.

Memory from upper right clockwise: A-P-T-M.

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Cardiac Shadow on PA Chest X-Ray

Right Border

Left Border

From above downwards:

1. Aortic knuckle
2. Pulmonary trunk / pulmonary conus
3. Left auricle
4. Left ventricle

Clinical points:

• Left atrial enlargement straightens or bulges the left auricular segment.
• Aortic knuckle becomes prominent with age, hypertension, and atherosclerosis.
• Right atrial enlargement increases the right lower cardiac border.

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Area of Superficial Cardiac Dullness

This is the part of the heart not covered by lung, mainly due to the cardiac notch of the left lung.

It overlies the right ventricle and gives dullness on percussion.

Loss of this dullness may occur in:

• Emphysema
• Left pneumothorax
• Lung hyperinflation

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Heart Sounds

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