Cardiac depression is one of the most common psychological reactions of patients with acute coronary syndrome (ACS). This study aimed to determine the prevalence of cardiac depression and its related factors among patients with ACS. This cross-sectional study was conducted during 2016 in patients with ACS who were admitted to hospitals affiliated to the Mazandaran University of Medical Sciences, Iran. In the present study, 407 patients completed the Cardiac Depression Scale (CDS) within two months (March -June). The data were analyzed by a chi-square test and a general linear model multivariate analysis. According to the results, the mean cardiac depression score in patients with ACS was 109.00 ± 16.49 (CI95: 107.39 to 110.60). Among the participants, 37 (9.1%), 72 (17.7%), and 298 (73.2%) patients had mild, moderate, and severe levels of depression, respectively. Although the two-way ANOVA was not significant, but there was a difference between cardiac depression score of a type of ACS. Given the high prevalence of cardiac depression among these patients, it is necessary to develop measures for routine screening in cardiac treatment units.