A combination of social inhibition and negative affectivity characterizes Type D personality. Type D, or distressed personality, is an established risk factor for the development and prognosis of coronary heart disease. It occurs in approximately 1 in 4 patients with coronary heart disease. This study aimed to investigate the relationship between Type D personality, illness perception, and coping strategies in patients undergoing open-heart surgery. This retrospective and cross-sectional study was conducted in a university hospital psychiatry and cardiovascular surgery clinics between February 2022 and April 2022. Seventy-one volunteered patients over the age of 18 who underwent open-heart surgery in the cardiovascular surgery clinic were included in the study. Cardiovascular surgeons recorded the sociodemographic and clinical data of the patients and referred them to the psychiatry clinic for further evaluation. Subsequently, patients underwent psychiatric evaluation and were assessed using the Type D Personality Scale, Coping Attitudes Assessment Scale, Hospital Anxiety and Depression Scale, and Illness Perception Questionnaire. According to this study, individuals with Type D personality tended to have higher scores on the Hospital Anxiety and Depression Scale. Analysis of the subdimensions of the Stress Coping Styles Scale revealed that individuals with Type D personalities showed a significantly lower optimistic approach and a considerably higher helpless approach. In terms of the subdimensions of the Illness Perception Questionnaire, it was found that individuals with Type D personality had a statistically lower treatment control approach and a statistically higher emotional representations approach. Identifying Type D personality traits in patients undergoing open-heart surgery can help manage negative illness perceptions through effective coping mechanisms.