- Subjects must be on optimal conventional heart failure therapy (with the exception of a beta-blocker), including an ACEI for at least 30 days prior to the Screening Visit, or the subject must have had a trial of an ACEI and proven to be intolerant, or the subject must be taking an ARB for at least 30 days prior to the Screening Visit or proved to be intolerant. Optimal conventional therapy may also include spironolactone, digitalis glycosides, diuretics, or other vasodilators.