 Patients with heart failure HF with reduced ejection fraction who qualify for the study will undergo a three-week run-in period in which any prior angiotensin-converting enzyme ACE inhibitor or angiotensin receptor blocker they were taking will be discontinued and they will be given valsartan 80 mg bid in a single-blind fashion. After the run-in, subjects will undergo four study periods in random order. During two study periods they will receive enalapril 10 mg bid and during two they will receive sacubitrilvalsartan LCZ696 200 mg bid for seven days. On the seventh day or each period, subjects will complete a study day in which they are randomized to receive either the bradykinin B2 receptor blocker icatibant or placebo intravenously. Each study period will be separated by a three-week washout during which subjects receive valsartan 80 mg bid. 