Several types of drugs are used to prevent blood clots or to treat blood clots after they have formed. Learn about them here., Blood clots can be very serious, so symptoms of blood clots should be evaluated by a doctor immediately. If not treated, a clot can break free and cause a pulmonary embolism—where the clot gets stuck in a blood vessel in the lung, causing severe shortness of breath and even sudden death. Treatment , If left untreated, a blood clot can reach your organs and cause potentially life threatening conditions, such as pulmonary embolism, stroke, or a heart attack., , , .