Recent reports have suggested that cytomegalovirus (CMV) infection may contribute to risk of cardiovascular disease. However, relationship between CMV infection and unstable angina (UA) is controversial and studies about this subject in Iran and even region are lacking. The aim of this study was to determine whether unstable angina is related to seropositivity to chronic cytomegalovirus infection. We measured serum CMV IgG levels in a case control study participants in CCU in Razi Hospital, Ahvaz, Iran, from 2004 to 2005. Blood samples were drawn during study period from 96 patients (mean age 56 years) with UA according to American Heart Association Criteria and from 96 participants free of cardiovascular disease (mean age 58 years) and stored at -20°C. Blood samples of patients were undertaken for investigating the specific anti CMV-IgG by ELISA method. Data were analyzed in SPSS 11.5 by using chi square test, odds ratios (OR) with 95% confidence intervals (CI). Ninety three percent of patients with unstable angina and 96.7% in the control group presented a positive anti CMV-IgG. Odds ratio was 0.52 with 95% CI: 0.10 to 2.42. There was no significant correlation between CMV-IgG positivity and unstable angina (P>0.05). There was also no differences in CMV-IgG positivity in clinical groups of UA (P>0.05). The relationship between seropositivity of CMV-IgG and unstable angina has been restituted by the results of this study. However, further population based cohort studies for relationship between CMV infection and coronary artery disease must be conducted.