Many heart failure patients retain excess water that can pool in their lungs, making it hard to breathe despite the best drugs available today. This is the congestion in "congestive heart failure." Fluid-reducing diuretics are the primary treatment for congestion. But diuretics prevent the kidneys from retaining salt, and indirectly eliminate their ability to retain water, so the drugs often do an imperfect job. When this happens, powerful intravenous diuretics are needed. But the kidneys cant tolerate a lot of diuretics, and kidney function worsens.