Instead of taking focus away from Emma, I decided to do an independent thread on heartworm, what it is, how it is contracted, and treatment.
The definitive site on heartworms is <http://www.heartwormsociety.org>
Dogs contract it by being bitten by a mosquito carrying the microfilaria. The microfilaria enter the blood stream and make their way to the heart where they lodge and grow into adults. It is endemic in most parts of the United States, with a few exceptions and isolated pockets of the country. Year round preventative should be given in most areas of the country. Now that dogs post hurricane Katrina have been scattered all over the US, heartworm is now appearing in areas where it didn't exist before and dogs that have lived in those areas all their lives are now coming up heartworm positive, much to their owners' dismay.
Dogs infected with heartworms can be asymptomatic for a while, but it is a slow and in the end painful death. Except for ivermectin sensitive breeds, such as collies, shelties, and a few others, treatment for heartworm involves a series of injections (usually immiticide which is basically a poison which kills the heartworms) spread out over a month to six weeks time, depending upon the severity of the load of worm a dog might be carrying, plus age, overall health and other extenuating factors. In the old days, arsenic was what was used and that was very hard on the dogs. Thankfully, immiticide was the drug of choice since I have been involved in dealing with heartworm positive dogs. It is still hard on the dogs being treated and veterinarian instructions must be followed.
As the worms start dying off they get into the blood stream to be carried through the body's cleansing system, it is possible for them to get lodged in the lungs or other organs and cause clots, which in turn can kill the dog. This is why there is limited activity allowed and essentially crate rest during the time of treatment. And not always will all the worms lodge in the heart. My vet told me of one dog where a worm had lodged at the base of the brain of a dog and it died during treatment. My second fosters, one of them was a heartworm positive and I lost her due to an aberrant worm that was lodged in her spin. She went down in her back and was paralyzed. Because of her, I am on pins and needles until I get the results of the heartworm test on a new foster and my gut will clinch if they come back positive. The good news is that every other one I have been through treatment with, they have sailed through with no problems at all.
There are alternative treatments as well and none should be done without veterinarian consultation. One protocol being utilized by rescue groups is just beginning the monthly preventative. The adult worms go through their life cycle and die off, the monthly preventative (which is something of a misnomer, as what it does is kill off any microfilaria that might be present preventing the development of adult worms to lodge in the heart) kills off any microfilaria preventing further investation. Alternative/holistic methods exist as well, again without veterinarian supervision, do not attempt on one's own.
While I am very sorry to hear Emma is having to go through this (and T-gal too), awareness has been raised and others will now have their corgis tested and put on preventative.
Cost wise, $100 +/- a year for preventative is a small price to pay to avoid more costly treatment and increased risk of losing one's corgi. Price for heartworm treatment varies around the country a bit, but the cost at my vet's is $300 - $400 per dog.