The fatal blow comes from complete blockage of blood flow through the heart, leading to what is called Vena Cava Syndrome. (mypetneedsthat.com)
Side effects include aneurysms, blood clots and even complete blockage of some blood vessels. (dachshund-owner-guide.com)
This would be more likely to shove chunks of dead worm farther into the arteries, creating a more complete blockage, increased pressure, and potential blow - out, bleeding into the lungs. (yourpetsbestfriend.com)