With prompt diagnosis and treatment, the majority of DVT’s are not life
threatening. However, a blood clot that forms in the invisible "deep veins" can be an immediate threat to your life, as compared to a clot that forms in the visible "superficial" veins, the ones beneath your skin. A clot that forms in the large, deep veins is more likely to break free and travel through the vein. It is then called an embolus.