What kind of hear failure?
Commonly, simply using diuretics to decrease blood volume can help a lot. Do you have a diagnosis of what the failure is from though as it really depends on what is wrong.
Here is a great page on heart failure in canine and treatments:
We lived with heart failure for over 2 years with Topper, he was on several meds but did well right up to the end. He started out with just lasix (diuretic) and theoplylline for the chronic brhonchitis that can go with it. About a year later we added spironlactone (human dose is one pill/day, we did 2, one morning and 1 evening). He had a very good year (maybe more, I lose track of time) then was filling up with fluid again, we added Vetmedin, which gave him another lease on life for about 6 or 8 months. My vet had told me that was the last resource we had.
So at the end, he was taking theophylline, lasix, spironlactone and vetmedin, all twice a day and he lasted well over 2 years from first diagnosis.