The purpose of this study is to test the hypothesis that the inhibition of the renin-angiotensin-aldosterone system (RAAS) with the angiotensin receptor blocker valsartan or the renin antagonist aliskiren will improve ventricular hemodynamics, as reflected by a greater reduction in levels of N-terminal proB-type natriuretic peptide (NT-proBNP) compared to placebo in subjects stabilized following acute coronary syndrome (ACS) who are determined to be at high risk due to an elevated concentration of natriuretic peptides.