Deep Vein Thrombosis (DVT) A blood clot in the leg can sometimes develop without obvious symptoms. Deep vein thrombosis occurs when a clot forms in the deep veins of the leg, often due to prolonged immobility, surgery, or certain medical conditions. Common signs may include swelling in one leg, pain in the calf, warmth in the affected area, or redness of the skin. Early detection is important because a clot may travel to the lungs and cause serious complications. If you notice unusual leg swelling or pain, seek medical evaluation with Dr Santosh Patil in Pune.