A blood clot forming in the superior vena cava, a major vein leading to the heart, may cause superior vena cava syndrome, which impedes the flow of blood to the heart, often with serious results, states WebMD. SVCS is most commonly associated with lung cancer and Non-Hodgkin lymphoma, or NHL.
Blood clots can travel to the heart, limbs, lungs, kidneys and brain, possibly causing a stroke, heart attack, organ damage or even death, according to the American Heart Association. Risk factors for excessive blood clotting include pregnancy, obesity and smoking. Additional risks come from long periods of bed rest, extended amounts of time sitting at a desk or while traveling, hormone replacement therapy and taking contraception medication. Genetic defects are a less common cause of excessive blood clotting, but may a diagnosed as a contributor if family members are known to have had dangerous blood clots or if there is a personal history of unexplained miscarriages or blood clots repeatedly diagnosed before age 40.
Pulmonary embolism can be caused by blood clots in deep veins, causing deep vein thrombosis, adds WebMD. However, it is most often associated with a blood clot that breaks loose in the leg and travels into the lung. Death can result if blood flow into the lung is completely blocked.