Heartworm treatment side effects

Question

Charlie   My dog, Charlie, is a 30lb. mutt who was recently rescued.  Upon rescuing him from a shelter I took him to a vet where he was quickly tested and confirmed positive for heartworms; Charlie has been undergoing treatment for his heartworms for about a month now.  When the treatment was started, the vet warned us of the high risk of clotting if Charlie becomes too active during his recuperation; I've tried asking for more details and researching the Internet, but no source has been able to clarify the symptoms of these clots that I should on the look out for.  I live in a calm apartment complex, with little going on inside or outside that could over stimulate Charlie, however it has been difficult to calm his attempts at playing though I do my best.  My biggest fear is that I'll miss the warning signs and not find him a vet the second a clot begins to form.   
Could you please help explain to me in "common people" language (instead of technical medical/vet terminology) the symptoms or signs of a clot resulting from heartworm treatment that I can be aware of?

Answer
Hi Caroline,
Your Charlie is quite the cutie pie. Your vet is correct about being careful with too much activity for him at this time.

The clotting that the vet is probably referring to is not so much a blood clot that starts the problem, but a chunk of dying worms that break loose and then land in the lungs forming a clot.

For the most part, coughing is going to be the first sign you will see/hear of any symptoms. If they were severe, he would also stagger, be unable to walk and be very weak.

Most dogs do very well through heartworm treatment. There are exceptions of course and there is no way of knowing how a dog will respond short-term.

Depending on the method your vet used for the injections, it does take about 3-6 months for the worms to die off and start to be absorbed by the body. This is the most dangerous, critical time. You don't want the dog breathing hard from running, playing, getting excited because that is what causes the heart to pump and possible break apart and dislodge these dying worms.

So you can see how it would be a risk. But the symptoms are pretty easy to spot- and they are as I said up above. If you notice him breathing hard, or coughing more than once or twice, or staggering around and being unable to walk well, then you should call the vet right away.  

It sounds like you are being as diligent as you can. I feel confident that Charlie will do well and live a long happy life.