★★★★★
Another thing you might want to check out is the amino acid Taurine. I remember reading somewhere that CHF can be caused by a Taurine deficiency (sorry I cannot remember where I read it). Try putting "taurine congestive heart failure" into a search engine.
As a point of reference, I have had two very large male cats die of heart failure and I strongly suspect that there wasn't enough taurine in the cat food for cats of their size. As another point of reference, the best food source for Taurine is...heart muscle!
