Background: Recent studies have suggested that there is a significant correlation between elevated serum Osteoprotegerin (OPG) levels and cardiovascular diseases. We investigated whether the serum OPG levels were associated with heart failure (HF), acute myocardial infarction (AMI) and unstable angina (UA), and whether the serum OPG levels were correlated with the NYHA classifications. Methods: Serum OPG was measured in 127 patients who were hospitalized in the cardiology department with HF, AMI and UA and they were compared to 63 controls. The NYHA classification was used to define the clinical disease severity. The serum OPG was measured by ELISA. Results: The serum OPG levels were significantly higher in the patients with HF and AMI than in the control subjects (p=0.003, p=0.002, respectively). The mean OPG levels were 555, 683, 774 and 856 pg/ml for the subjects and controls by NYHA classification II,III,IV respectively. Multiple regression analysis revealed that the serum OPG levels were significantly associated with HF and AMI, and when all subjects were regrouped according to NYHA classification, also with the NYHA classification. Conclusion: The serum OPG levels were increased in patients with cardiovascular disease such as HF and AMI, and with the NYHA classification in Asian subjects and could be a marker for different stages of cardiovascular disease