Deep vein thrombosis (DVT) is a condition in which a blood clot forms in a deep vein, most commonly in the legs. These veins are located beneath the surface of the skin and are responsible for returning blood to the heart. When a clot (thrombus) develops, it can partially or completely block blood flow, leading to swelling, pain, and inflammation.

In some cases, DVT may cause no obvious symptoms, making it difficult to detect. When present, symptoms can include leg swelling, tenderness, warmth, and a heavy or aching sensation, usually in one leg. DVT is considered a medical emergency because the clot can dislodge and travel to the lungs, causing a pulmonary embolism (PE)—a life-threatening condition.

Risk factors include immobility (such as after surgery or long flights), trauma, recent hospitalisation, cancer, pregnancy, hormonal therapy, or inherited clotting disorders.

Diagnosis is confirmed with imaging, typically a venous Doppler ultrasound. Treatment includes anticoagulant medications, compression therapy, and in selected cases, clot removal procedures. Early diagnosis and treatment are essential to prevent complications and long-term effects such as post-thrombotic syndrome, which can cause chronic leg swelling and discomfort.