Surface anatomy of the heart describes the external projections of cardiac structures onto the chest wall. These landmarks are essential for physical examination, cardiac auscultation, electrocardiogram lead placement, and emergency procedures such as pericardiocentesis.
Anatomical Position
The heart lies within the mediastinum, between the lungs, with its long axis oriented from the right shoulder toward the left hip. Approximately two-thirds of the heart lies to the left of the midline.
The heart is positioned:
- Posterior to: The sternum and costal cartilages
- Anterior to: The thoracic vertebrae (T5-T8)
- Superior to: The diaphragm
- Between: The pleural cavities (medial mediastinum)
Surface Projections of the Heart
The cardiac silhouette projects onto the anterior chest wall as an irregular trapezoid or triangle bounded by four points:
The Four Cardinal Points
| Point | Location | Structure |
|---|---|---|
| Right superior | Right 3rd costal cartilage, 1 cm from sternal edge | Superior vena cava/right atrium |
| Right inferior | Right 6th costal cartilage, 1 cm from sternal edge | Right atrium/inferior vena cava |
| Left superior | Left 2nd intercostal space, 2 cm from sternal edge | Pulmonary trunk |
| Left inferior (apex) | Left 5th intercostal space, 7-9 cm from midline (midclavicular line) | Left ventricular apex |
Right Border
- Formed by the right atrium
- Extends from the right 3rd to right 6th costal cartilage
- Approximately 1-2 cm right of the sternal edge
- The superior vena cava enters the right atrium at the upper end
- The inferior vena cava enters at the lower end
Left Border
- Formed by the left ventricle (with the left atrial appendage at the upper portion)
- Extends from the left 2nd intercostal space to the apex
- Curves convexly leftward and inferiorly
- The pulmonary trunk occupies the uppermost portion
Inferior Border
- Formed primarily by the right ventricle
- Extends from the right 6th costal cartilage to the apex
- Runs nearly horizontally
- Lies on the diaphragm
Superior Border
- Formed by the atria and great vessels
- Extends horizontally from the left 2nd to right 3rd costal cartilages
- Includes the superior vena cava, ascending aorta, and pulmonary trunk
Surface Projection of Cardiac Chambers
| Chamber | Surface Projection |
|---|---|
| Right atrium | Right border, from 3rd to 6th right costal cartilage |
| Right ventricle | Most of the anterior surface, behind the sternum and left 4th-5th costal cartilages |
| Left atrium | Posterior (not on anterior surface), projects to the left of T5-T8 vertebrae |
| Left ventricle | Left border and apex, behind left 3rd-5th costal cartilages |
Surface Projection of Cardiac Valves
The cardiac valves do not project directly at their auscultation points. The valve projections are clustered near the sternum, while the auscultation areas follow the direction of blood flow.
Valve Projection Points (Anatomic)
| Valve | Surface Projection | Intercostal Space |
|---|---|---|
| Aortic valve | Left 3rd intercostal space, at sternal edge | Behind left 3rd costal cartilage |
| Pulmonary valve | Left 2nd intercostal space, at sternal edge | Behind left 2nd costal cartilage |
| Tricuspid valve | Left 4th intercostal space, at sternal edge | Behind right 4th costal cartilage |
| Mitral valve | Left 4th intercostal space, at sternal edge | Behind left 4th costal cartilage |
Auscultation Areas
Auscultation points are selected to best hear valve sounds based on the direction of blood flow and the proximity of the chamber receiving blood:
| Valve | Auscultation Area | Location |
|---|---|---|
| Aortic | Right upper sternal border (Aortic area) | Right 2nd intercostal space |
| Aortic (alternate) | Left upper sternal border (Erb point) | Left 3rd intercostal space |
| Pulmonary | Left upper sternal border (Pulmonary area) | Left 2nd intercostal space |
| Tricuspid | Left lower sternal border (Tricuspid area) | Left 4th-5th intercostal space |
| Mitral | Left midclavicular line (Mitral area/apex) | Left 5th intercostal space |
Coronary Artery Surface Projections
| Artery | Surface Path |
|---|---|
| Left main | From left aortic sinus, behind pulmonary trunk |
| Left anterior descending (LAD) | Descends in anterior interventricular groove toward apex |
| Left circumflex (LCx) | Passes in left atrioventricular groove |
| Right coronary (RCA) | From right aortic sinus, passes in right atrioventricular groove |
| Posterior descending (PDA) | Descends in posterior interventricular groove |
Surface Landmarks for Clinical Procedures
Pericardiocentesis
The safest approach to access the pericardial space:
Subxiphoid approach:
- Insertion point: Angle between the xiphoid process and left costal margin
- Needle angle: 15-30 degrees posterior to the sternum
- Direction: Toward the left shoulder (tip of the scapula)
- Depth: 3-5 cm (variable)
Parasternal approach (alternative):
- Insertion point: Left 5th intercostal space, at sternal edge
- Avoids the internal thoracic artery (1-2 cm lateral to sternum)
Chest Tube Insertion
For pericardial or pleural drainage:
- Safe triangle: Bordered by the lateral edge of pectoralis major, the lateral edge of latissimus dorsi, the 5th intercostal space superiorly (nipple level in men), and the 6th intercostal space inferiorly
CPR Hand Position
- Compression point: Center of the chest, on the lower half of the sternum
- Corresponds to the left ventricle underlying the sternum
- Avoid placing hands over the xiphoid process
Electrocardiogram Lead Placement
| Lead | Position |
|---|---|
| V1 | Right 4th intercostal space, sternal edge |
| V2 | Left 4th intercostal space, sternal edge |
| V3 | Midway between V2 and V4 |
| V4 | Left 5th intercostal space, midclavicular line |
| V5 | Left 5th intercostal space, anterior axillary line |
| V6 | Left 5th intercostal space, midaxillary line |
Cardiac Borders on Chest Radiography
Posteroanterior (PA) View
| Border | Structure |
|---|---|
| Right upper | Superior vena cava |
| Right lower | Right atrium |
| Left upper | Aortic knuckle (aortic arch) |
| Left middle | Main pulmonary artery |
| Left lower | Left ventricle |
Lateral View
| Structure | Location |
|---|---|
| Anterior border | Right ventricle (retrosternal) |
| Posterior border | Left atrium and left ventricle |
| Inferior border | Diaphragm |
| Posterior esophageal impression | Left atrium (normal, mild) |
Age-Related Changes in Surface Anatomy
- Neonates: Heart is more horizontal, apex at left 4th intercostal space
- Children: Heart more vertical, apex at left 5th intercostal space
- Adults: Heart position varies with body habitus
- Elderly: Heart may descend, aorta may dilate and become tortuous
- Pregnancy: Heart displaced upward and leftward
Body Habitus Variations
| Habitus | Heart Orientation | Apex Location |
|---|---|---|
| Tall, thin (asthenic) | Vertical, central | Left 5th-6th intercostal space, near midclavicular line |
| Short, stocky (hypersthenic) | Horizontal, leftward | Left 4th-5th intercostal space, lateral to midclavicular line |
| Average (sthenic) | Oblique | Left 5th intercostal space, midclavicular line |
Clinical Importance of Surface Anatomy
Knowing the surface anatomy allows the clinician to:
- Locate the apex beat (tactile assessment of left ventricular contraction)
- Identify the point of maximal impulse (PMI)
- Properly auscultate heart sounds and murmurs
- Place ECG leads consistently
- Perform pericardiocentesis safely
- Interpret chest radiographs accurately
- Guide emergency thoracotomy incisions