The purpose of this study is to discover whether the inhibition of the xanthine oxidase with allopurinol leads to a reduction of the production of oxygen free radicals in patients with CHF and thereby improves characteristics of oxydative metabolism, peripheral blood flow, immune function and functional status.

Inclusion Criteria:

• The patient is a male and at least 21 years of age.
• The patient has clinical evidence of heart failure: a) reduced ejection fraction (≤40%) or cardiomegaly on CXR or left ventricular impairment on echocardiography (LVEDD ≥60mm), b) stable clinical condition and medication for at least 1 month prior to the study.
• No history of unstable angina, myocardial infarction or stroke within 3 months prior to the study.
• The patient is receiving full conventional medical therapy for heart failure (ACE inhibitor or angiotensin II blocker, diuretics etc.).
• The patient is willing and capable of complying with the requirements of this protocol.
• The patient has provided written informed consent .

Exclusion Criteria:

• The patient has any life-threatening disease, other than heart failure (including patients with known, or suspected, myocarditis or with automatic implantable cardioverter/defibrillators).
• The patient has an active malignancy of any type, or history of a malignancy (Patients who have a history of basal cell carcinoma that has been surgically removed are acceptable). Patients with a history of other malignancies that have been surgically removed and who have no evidence of recurrence for at least five years prior to study enrolment are also acceptable.
• The patient has had a heart transplant.
• The patient has severe renal disease (S-Creatinine >300 μmol/l), severe liver disease (ASAT or ALAT > 3 times of upper limit of normal range), rheumatoid arthritis, or complains of gout.
• The patients has received allopurinol therapy previously or if he is known to suffer from gout (acutely or chronically).
• The patient has an exercise capacity of > 20 ml/kg/min (treadmill, Bruce protocol) or is in functional NYHA class I.