Q. Do smaller bread of dogs have a harder time surviving heart worms than big dogs?
DESTINI R. HOLLOWAY, DVM
A. No they sure don't . The prognosis for any type of heart disease depends on the exact abnormality that is present. Myxomatous valvular disease and mitral valve insufficiency are the most common among small breed animals and can usually be managed well. It is not until your pet shows early signs of heart failure that medications will be recommended to help the heart because it is no longer able to compensate for the defect.
So to gather more information about your particular pets disease I would recommend a full cardiac work up of chest x-rays and possibly an echo if needed to find out exactly what part of your pet's heart is defective, so that you have a better idea of his prognosis.