Human Heart Anatomy: Location, Structure, and Function

Where Is the Heart?

The heart resides in the mediastinum—the central compartment of the thoracic cavity—slightly left of the midline. It sits posterior to the sternum, anterior to the vertebral column (T5–T8), and between the lungs. The apex points inferiorly, anteriorly, and to the left.

Protective Enclosures

• Pericardium: Double-walled sac (fibrous outer, serous inner)
• Pericardial cavity: Lubricating fluid reduces friction
• Rib cage & sternum: Bony shield

Size & Weight

• Dimensions: ~12 cm (L) × 8 cm (W) × 6 cm (AP) — roughly a clenched fist
• Weight: 280–340 g (10–12 oz) in adults; larger in athletes

Four Chambers & Flow

Cardiac Cycle

• Systole: Contraction (ejection)
• Diastole: Relaxation (filling)
• Heart rate: 60–100 bpm at rest (adults)
• Cardiac output: ~5 L/min at rest

Electrical Conduction

SA node → AV node → Bundle of His → Bundle branches → Purkinje fibers → coordinated contraction.