What is a saddle thrombus: A thrombus is a clot that forms in the bloodstream, in this case usually in the heart. When it’s dislodged from the heart and enters the aorta it ends up lodging itself at the bifurcation of this large artery as it branches off into the smaller arteries that supply blood to the hind limbs. When it gets stuck it’s now called an embolism, and the result in the case of a saddle thrombus (an embolism at the base of the aorta) is that it cuts off the main blood supply to the back legs; an extremely painful condition.