Coughing may be a sign of severe heart disease in which fluid has built up in, or around, the lungs (a condition known as Congestive Heart Failure). Cough can also be due to pneumonia, heartworms, lungworms, collapsing trachea, bronchitis, lung cancer, and many other disorders that can only be diagnosed by chest X-rays and other testing.
In dogs who have already been diagnosed with congestive heart failure and who are on furosemide, worsening coughing and or difficulty breathing may indicate more fluid accumulation and more furosemide may be required. Ask your veterinarian whether it is alright to give an additional dose of furosemide for worsening cough. Pay attention to the timing and duration of cough (for example, if the cough worsens after excitement, after eating or drinking, or at night) as this information can help your veterinarian better diagnose and treat your animal's cough. Cough is less often due to heart disease in cats, although heartworm disease, asthma, bronchitis and lungworms are all common causes of cough in cats. Severe cough, especially with difficulty breathing, can be an emergency situation and veterinary care should be sought immediately.