In order to be considered eligible subjects, the following entry criteria must be met:

• At least 18 years of age
• ischemic or nonischemic cardiomyopathy
• NYHA Class III or IV
• one hospitalization, or two outpatient visits, for the treatment of worsening heart failure within 12 months requiring the administration of I.V. heart failure therapy
• LVEDD >3.2 cm/m2 or >=6.0 cm
• LVEF of less than or equal to 30%
• concomitant treatment with optimal conventional heart failure therapy

Exclusion Criteria

Subjects who meet any one of the following criteria will be deemed ineligible for participation in the study:

Subjects on the following concomitant medications:

• Calcium antagonists other than amlodipine or felodipine
• Flecainide, encainide, propafenone, dofetilide or disopyramide
• Subjects receiving I.V. positive inotropic agents within seven days of the Screening Visit or Randomization Visit
• Subjects receiving a human B-type natriuretic peptide, including nesiritide, within seven days of the Screening Visit or Randomization Visit

• Subjects receiving oral or I.V. phosphodiesterase III inhibitors (PDEI III), including levosimendan and cilostazol, within seven days of the Screening Visit or Randomization Visit

  • Subjects with active hepatic (screening serum total bilirubin >= 3.0 mg/dl (>=51.3 umol/l), renal (screening serum creatinine >= 2.0 mg/dl (=178.8 umol/l)), hematologic, gastrointestinal, immunologic, endocrine, metabolic, or central nervous system disease
  • Subjects with a serum potassium <4.0 mEq/L or >5.5 mEq/L (<4.0 mmol/l or >5.5 mmol/l) at Randomization Visit
  • Subjects with a magnesium level of <1.0 mEq/L (<0.5 mmol/l) at Randomization Visit (Visit 0)
  • Subjects with a serum digoxin of >1.2 ng/ml (>1.5 nmol/l) or a serum digitoxin of >20 ng/ml (>26.2 nmol/l) at the Randomization Visit are excluded. A target serum digoxin level of <=1.0 ng/ml (<=1.3 nmol/l) is recommended