Heart Anatomy: Precise Location, Orientation, and Surface Projections in the Thorax

The heart lies in the middle mediastinum, within the pericardial sac, oriented obliquely—apex pointing inferiorly, anteriorly, and leftward; base facing posteriorly, superiorly, and rightward.

Surface Landmarks (Clinical Anatomy)

Borders (Projected on Anterior Chest Wall)

• Right border: Right 3rd costal cartilage → right 6th costal cartilage (1 cm lateral to sternum).
• Inferior border: Right 6th costal cartilage → apex (5th ICS, midclavicular line).
• Left border: Left 2nd costal cartilage → apex (curves laterally).
• Superior border (base): Left 2nd → right 3rd costal cartilage (behind sternum).

Key Points

• Apex beat (PMI): 5th intercostal space (ICS), 1–1.5 cm medial to midclavicular line (MCL). Palpable in 70% adults.
• Base: Level of 2nd–3rd costal cartilages; receives great vessels.
• Right atrium: Right border; receives SVC/IVC.
• Left ventricle: Apex + inferior border; pumps systemic circulation.
• Right ventricle: Anterior surface; pumps pulmonary circulation.

Valves & Auscultation Points

Valve	Surface Projection	Auscultation
Aortic	Right 2nd ICS, sternal border	Right 2nd ICS
Pulmonic	Left 2nd ICS, sternal border	Left 2nd ICS
Tricuspid	Left 4th–5th ICS, sternal border	Left 4th–5th ICS
Mitral (Apex)	5th ICS, MCL	5th ICS, MCL (apex)

Anatomical Relations

• Anterior: Sternum, thymus, costal cartilages 3–6.
• Posterior: Esophagus, descending aorta, thoracic vertebrae T5–T8.
• Right lateral: Right lung/pleura, phrenic nerve, SVC.
• Left lateral: Left lung/pleura, phrenic nerve.
• Inferior (diaphragmatic surface): Diaphragm (central tendon), liver (right), stomach (left).

Variants

• Dextrocardia: Heart on right (mirror-image or isolated).
• Situs inversus totalis: All viscera mirrored (1:10,000).
• Pectus excavatum/carinatum: Displaces heart leftward/posteriorly.

Surface anatomy guides physical exam, pericardiocentesis, pacemaker placement, and imaging interpretation.