Can having heartworms cause a dog to have an enlarged heart after they are cured?

I adopted Maggie, my 8 year old beagle mix, from my vet 7 years ago. She was a stray and when they found her, she had heartworms. She was successfully treated and has been doing well up to 4 weeks ago. Around that time, she started coughing and seemed very lethagaric. On our vet visit 4 weeks ago, the doctor took x-rays which showed an enlarged heart and fluid. He also said he detected a moderate heart murmur. (On Maggie's annual vet visit 6 months ago, the vet did not hear a murmur.) The vet prescribed lasix and enalapril maleate to treat congestive heart failure. Last week on a re-check, he added theophylline to her treatment since her symptoms had not improved. This morning, Maggie had an EKG which was normal and more x-rays were done (no change in enlarged heart). We are now waiting for results from this morning's blood draw. The vet now thinks that Maggie may have allergies and not heart disease. Could she have always had an enlarged heart due to the past heartworms?

Obviously this is a good question for the vet, but as a moderately education person, I would say it makes sense that an enlarged heart could result from having had heart worm (even if successfully treated) because the heart worm invades the heart muscle and it would seem that damage would most likely be caused by this and the degree would be determined by how long the dog was sick before treatment was begun and the overall health of the dog before it got sick. Like in a human when you have an injury to a joint or something and then get arthritis later in life that joint tends to have it worse than other areas. Good luck and God Bless.

I cannot recall any enlarged hearts post successful heartworm treatment but then again we didn't xray all prior or post treatment. There can be residual effects after heartworm treatment. the murmur may not have been evident 6months ago. Could she be older than you think she is? Sometimes these things are just luck of the draw. That you have so many questions is good and perhaps you would feel better with a second opinion. Maggie is still a lucky dog to have found a family that takes such good care of her.