This randomized, double blind, placebo-controlled study of high-dose spironolactone vs. placebo (for patients not receiving MRA at home) or low-dose spironolactone (for patients already receiving low-dose spironolactone) in AHF, will enroll 360 participants at approximately 30 clinical centers. After obtaining informed consent, subjects who fulfill all the inclusion criteria and none of the exclusion criteria will be randomized. Randomization will be performed by using procedures determined by the Coordinating Center (CC).