What is the problem with my cat's heart?

So a few days ago my cat went to the vet to get a bath, shots, etc.. The vet said he had a heart murmur, which was harmless. He has had some labored breathing and short bouts of coughing since then. He barfed (unfortunately on my bed and foot in a sock xD) and then his breathing sounded a LITTLE better. The internet says it could be a heart worm.I guess my main question is: Do heart worm medications KILL heart worms? Or just PREVENT heart worm infections? Also, about how much would it cost to get the heart worm killed/removed/fixed?Thanks!

Heart worms are rare in cats. If he has a murmur, that could be an early sign of congestive heart failure. The best thing to do would be to take him back to the vet for an X-ray and possibly further diagnostics to see what the issue is. The monthly heart worm pills are only to prevent. A different medication is used to kill heart worms. If an animal has heart worms and takes the preventative, the preventative could make the animal sick or even kill it, but again, heart worms are rare in cats.

Actually, heartworms are NOT rare in cats - they are what my one vet calls "under diagnosed". If you live in an area where dogs are routinely given heartworm preventative, then your cat is at risk also. Unlike dogs, there is no medication to kill/remove the heartworm. It's a period where the condition is managed with steroids to reduce the inflammation, and waiting it out until the worm dies, breaks up, and is eventually expelled, bit by bit. It's only diagnosed with a blood test. The only thing you can do is prevent heartworm with a product like Revolution or Advantage Multi (both available only from your vet). It's not normal for cats to cough. They can cough from a bronchial infection, asthma, heartworm, and heart disease. If he continues to cough, then he needs to go back to the vet. Some heart murmurs are harmless, others indicate heart disease. It takes further diagnostics to determine what the cough is from. Give it a week - if he's still coughing then make another vet appointment.