The purpose of this study is to evaluate the impact of genetic variations on the response to candesartan in patients with heart failure who are already treated with an ACE inhibitor.

Principal Inclusion Criteria:

1. Male or female > or = 18 years old.
2. Symptomatic CHF corresponding to NYHA class II-IV symptoms for at least 4 weeks prior randomization.
3. LVEF < or = 40%
4. Treatment with an optimal and stable dose of ACE inhibitor for at least 4 weeks prior to enrolment in the study.

Principal Exclusion Criteria:

1. Treatment with an ARB within 8 weeks prior to randomization.
2. Known hypersensitivity to ARBs or ACE inhibitors.
3. Creatinine clearance < 30 ml/min or serum creatinine > 221
4. Current serum potassium > or = 5.0 mmol/L or a history of marked ACE inhibitor or ARB induced hyperkalemia.
5. Known bilateral renal artery stenosis.
6. Current symptomatic hypotension and/or systolic B.P. < 90 mmHg.
7. Decompensated heart failure described as hospitalization or I.V. administration of medication in emergency room or heart failure clinic within 4 weeks
8. Stroke, acute coronary syndrome, PCI within the last 4 weeks before randomization.
9. Connective tissue disease or chronic inflammatory condition
10. Acute inflammatory process such as an infection or gout attack in the last 2 weeks.
11. Pregnant or lactating women or women of childbearing potential who are not protected from pregnancy by an accepted method of contraception.