What are the different stages of heartworm disease?

There are four stages of heartworm disease. Stage one is the asymptomatic stage, where the dog has been infected but is not showing any symptoms. Stage two might involve the dog being listless, having a slight exercise intolerance, or being more lethargic than usual. Stage three is characterized by coughing, possible flecks of blood in the cough, and more pronounced exercise intolerance and lethargy. Stage four involves heart failure, a swollen belly, persistent coughing, and extreme lethargy.

There are four different stages of heartworm disease. Stage one is when the dog is infected with the larvae, and you might not even notice anything at this point. Stage two is characterized by a bit of exercise intolerance and a mild cough. Stage three is more severe, with a much more hacking cough and an increased amount of exercise intolerance. Stage four is the worst stage, where the dog may exhibit severe exercise intolerance, and sometimes even collapse. At this stage, the dog is most likely in congestive heart failure and it can even lead to death.