Background: About 19% to 66% of patients develop depressive or anxiety disorder, and 10% to 20% develop posttraumatic stress disorder (PTSD) after acute coronary syndrome (ACS). Various psychological factors are involved in development of such psychiatric disorders (personalilty traits, coping style, defence mechanisms, acute stressors, etc.). Kellerman's psychodynamic model is the basis of this research since it links specific emotions and defense mechanisms. ----- Objectives: To investigate the development of psychiatric disorders in patients with ACS, defense mechanisms and dimensions of personality of the subjects with ACS, and changes in defense mechanisms and dimensions of personality retesting them after one month and after 6 months. ----- Materials and methods: Research has been conducted in three phases: the 1st after stabilization of acute coronary syndrome, the 2nd after one month and the 3rd after six months. The first phase of the study included 121 subjects, the second phase included 80 subjects and the third phase 56 subjects. Defense mechanisms were measured with the Life Style Inventory (LSI), while dimensions of personality were measured by Emotions Profile Index (EPI). Psychiatric disorders were diagnosed using the Mini International Neuropsychiatric Inventory (MINI). ----- Results: In the second phase of the study 27,5% of the subjects had acute stress disorder (ASP), 13,8% had major depressive disorder (MDD), while 10% had comorbidity of MDD and ASP. 10% In the third phase MDD was diagnosed in 21,4% of subjects, PTSD in 26,76%, and comorbidity of MDD and PTSD in 14,5% of the subjects. Defense mechanism repression is a significant predictor for the development of MDD in the second and the third phase and of PTSD in the third phase of research. There were statistically significant differences in the use of negation, regression, projection, and intellectualization during the three phases of research. Level of general defensive orientation in all 3 phases is within the optimal range, and there is a trend of decline in the second and the third phase. Personality dimensions were stable throughout the study period. A group profile of subjects matches the profile of the normal population. ----- Conclusion: The dimensions of personality are stable over 3 phases of research. STE-ACS patients are using negation, intellectualisation, regression, and projection, while NSTE-ACS patients are using intellectualisation and regression. A statistically significant difference was found in the manifestation of these defense mechanisms in the first phase while in other phases their manifestation is stable. Repression is a statistically significant predictor for the development of MDD in the second and third phase, and PTSD in third phase. NSTE-ACS patients who develop PTSD manifest personal dimension of deprivation (type D personality), and the defense mechanisms regression and intellectualisation. Findings of this research represent another contribution to the early identification of high risk patients for development of post-ACS depressive or anxiety disorders. They could also help to improve prevention of such disturbances as well as development of individualized methods of treatment.