Symptoms of a blood clot in the venous system can include swelling of the affected area, warmth, redness, and pain. Venous blood clots occur most commonly in the arms and legs. Symptoms of an arterial blood clot result from a lack of or decrease in oxygen delivery to the tissues supplied by the involved artery. Pain in the involved area is often the first symptom. Other symptoms can occur when arterial clots form in a particular area. For example, clots in the coronary arteries can cause chest pain and the accompanying symptoms of a heart attack. If a clot forms in an artery of the brain, a stroke can occur, which can cause a number of different symptoms, depending on the precise area of the brain that is affected. Clots in the extremities can cause a pallor or whitening of the area, weakness, loss of sensation, or paralysis. Clots in the intestinal arteries can cause intense pain and bloody diarrhea.