I think it's because the heart is pumping enough, especially with HF patients. I had difficulty breathing but It was because I had blood clots in both of my lungs, especially when I laid on my back. I dont know if it helps but I drink one half gallon of water every day. Not at one time, but I sip through-out the day. Of course, I have to get up before day break, but it's worth it. I try to avoid salt but we need it, so when I do use it, I use very little. It's hard to break that habit with salt and sugar.