Surface Markings and Cardiac Shadow of the Heart

Surface Markings of the Heart (4 Reference Points)

The outline of the heart can be marked on the chest wall using four reference points connected by lines:

Point	Location
Upper right	Upper border of right 3rd costal cartilage, 1 cm from the median plane
Upper left	Lower border of left 2nd costal cartilage, 1.5 cm from the median plane
Lower right	Right 6th costal cartilage, 1.5 cm from the median plane (near xiphisternal joint)
Lower left (apex)	Left 5th intercostal space, 9 cm from the midsternal line (just medial to midclavicular line)

• Right border: Nearly vertical line connecting upper right to lower right — formed by the right atrium
• Left border: Curved line from upper left to lower left (apex) — formed by the left ventricle (mainly) + left auricle
• Inferior border: Nearly horizontal line from lower right to the apex — formed by the right ventricle
• Upper border: Oblique line connecting upper right to upper left — formed by both atria (mainly left)

Surface Markings of Cardiac Valves

All four valves lie on an oblique line running from the 3rd left costal cartilage to the 6th right costal cartilage, posterior to the sternum.

Valve	Surface Marking
Pulmonary valve	Behind the medial end of the left 3rd costal cartilage and adjoining sternum (horizontal line, 2.5 cm)
Aortic valve	Behind the left half of the sternum opposite the 3rd intercostal space (slightly oblique, 2.5 cm)
Mitral valve	Behind the left half of the sternum opposite the left 4th costal cartilage (oblique, 3 cm)
Tricuspid valve	Behind the right half of the sternum opposite the 4th and 5th intercostal spaces (vertical oblique, 4 cm)

Auscultatory Areas

Valve sounds are best heard not directly over the valve but at auscultatory areas — in the direction of blood flow through the valve.

Valve	Auscultatory Area
Pulmonary	2nd left intercostal space near the sternum
Aortic	2nd right intercostal space near the sternum
Mitral	Left 5th intercostal space, 9 cm from midline (apex beat — over apex of heart)
Tricuspid	Right half of the lower end of the body of the sternum

Mnemonic for valve order (apex to base): “Try Pulling My Aorta” — Tricuspid, Pulmonary, Mitral, Aortic

Cardiac Shadow in PA Chest Radiograph

In the PA chest X-ray, the mediastinal shadow represents the cardiac silhouette.

Right Border of Cardiac Shadow (from above downwards)

1. Superior vena cava — upper part
2. Right atrium — lower part

Left Border of Cardiac Shadow (from above downwards)

1. Aortic knuckle — projection of the arch of aorta (becomes prominent in old age/atherosclerosis)
2. Pulmonary conus (pulmonary trunk)
3. Left auricle — normally a straight or slightly concave segment (straightens or bulges in left atrial enlargement)
4. Left ventricle — lowest and largest component

In mitral stenosis: the left auricle enlarges and straightens (or bulges) the middle segment of the left cardiac border.

Heart Sounds and Valve Closure

Sound	Closure	Heard as
First heart sound (S1)	Closure of atrioventricular valves (tricuspid + mitral) at start of ventricular systole	”LUB”
Second heart sound (S2)	Closure of semilunar valves (aortic + pulmonary) at start of ventricular diastole	”DUB”