The primary objective of this study is assess the effect of initiating sacubitril and valsartan tablets (Entresto) vs. enalapril in patients who are admitted with decompensated congestive heart failure by measuring changes in NT-proBNP levels during the course of the study. Potential patients are those with a history of heart failure with a weakened heart muscle. Once enrolled subjects will be randomized to receive either sacubitril and valsartan or enalapril and will take along with their other regularly prescribed medications. Subjects will have 9 visits of a period of 12 weeks, the first 8 weeks they not know which treatment they are receiving but the final four weeks all subject receive the sacubitril and valsartan. Each study visit will take about 90 minutes. Study medication and study related treatment will be provided at no extra cost to the subject.