Purpose: The objectives amongst cardiac patients with and without type 2 diabetes were to (i) describe self-reported characteristics as health-related quality of life (HRQoL), health behaviour, body mass index (BMI) and physical shape and to (ii) investigate the association between self-reported characteristics and 1- and 3-year mortality. Methods: Adult patients (≥ 18 years) discharged with a cardiac diagnosis were invited to participate in a national survey, DenHeart. Self-reported characteristics included HRQoL (EQ-5D-5L and HeartQol), health behaviour (alcohol and smoking), BMI and physical shape. Data were linked to national registries. The association between self-reported characteristics and 1- and 3-year mortality were investigated using the Cox Proportional Hazard Regression model, reported as hazard ratios (HR) with 95% confidence intervals (CI). Results: In total, 16,659 cardiac responders were included (n = 2,205 with type 2 diabetes, n = 14,454 without type 2 diabetes). Self-reported characteristics were worse amongst cardiac patients with type 2 diabetes compared to those without. After three years, the mortality rate was 14% amongst responders with diabetes and 7% amongst responders without type 2 diabetes (p ≤ 0.001). Better HRQoL was associated with a reduced risk of mortality amongst both groups. “Never been smoking” significantly reduced the risk of 1- and 3-year mortality amongst cardiac patients without diabetes, whereas good physical shape was associated with a reduced risk across both groups. Conclusion: HRQoL, health behaviour, BMI and physical shape are significantly worse amongst cardiac patients with type 2 diabetes. Better HRQoL was associated with a reduced risk of mortality amongst both groups, whereas other self-reported characteristics and the mortality risk varied.