Deep vein thrombosis (DVT) usually occurs in your thighs or calf muscles when a blood clot is situated within a deep vein in the muscle. The restricted blood flow often causes pain and swelling (though symptoms only occur in about fifty percent of cases). If these clots break free, they can cause damage to organs and other blood vessels. If a clot should travel to your heart or lungs, it can potentially cause an untimely death. This is a life-threatening condition is known as a pulmonary embolism, and symptoms include coughing of blood, shortness of breath, dizziness, and various levels of pain.