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1 When blood clots occur in a vein, symptoms may include. 2  pain, 3  swelling, 4  warmth, and. 5  redness. 6  If a forms in a vein in a leg or arm breaks; breaks off and travels to the lung a pulmonary embolus can occur. 7  Symptoms of pulmonary embolism are chest pain and shortness of breath.
Quick Answer. Large blood clots in the legs can cause symptoms such as leg redness and warmth, leg swelling, and leg pain that worsens when standing up or walking, according to ClotCare. While blood clots located below the knee are unlikely to cause complications, clots that start or extend above the knee sometimes break away, travel through the blood and block blood vessels in the lungs, causing a pulmonary embolism.