Few studies assess the role of personality styles in predicting the onset of depression among cardiac patients. This study evaluates whether temperament and character can represent a risk factor for the development of incident first-ever depressive episodes in patients at their first acute coronary syndrome (ACS). Two hundred sixty-seven (72.1%) subjects (male) completed the Temperament and Character Inventory (TCI) a few days after the cardiac event. At baseline and after 1, 2, 4, 6, 9, 12, and 24 months of follow-up, the participants completed the Primary Care Evaluation of Mental Disorder (PRIME-MD) and the Hospital Anxiety and Depression Scale to establish the presence of a depressive episode and its severity. During the follow-up, 61 (22.8%) participants developed a depressive episode. Temperamental risk factors for incident depression were scored high on novelty seeking and harm avoidance at the TCI. Given the detrimental effect of depression on cardiac prognosis, clinicians should take temperament variables into account when determining the treatment plans of their patients with ACS.