Newly infested dogs typically do not exhibit signs of heartworm disease for several months, according to Pet MD. As the disease progresses, heartworms cause damage to the heart and lungs. The damage caused by heartworms can cause a number of issues such as enlarged liver, fluid accumulation in the abdomen, breathing difficulties and elevated blood pressure, according to The American Heartworm Society. Abrupt death often occurs in dogs with advanced stages of heartworm disease.
