Objective: To explore (i) the prevalence of cardiac risk factors (obesity, smoking, excessive alcohol consumption and medication non-adherence) among cardiac patients with depression and anxiety, (ii) associations between depression and anxiety scores and cardiac risk factors and (iii) the association of depression and anxiety and cardiac risk factors with mortality, and their population attributable risk. Methods: A national cross-sectional study using patient-reported outcomes at discharge and national register data. For one year (April 15th 2013 to April 15th 2014) all patients discharged or transferred from the five Danish Heart Centres were included in the study. A total of 14,239 patients answered the HADS questionnaire, response rate 51%. Results: Mean age was 64.8 years and 69% were male. Patients with depression or anxiety (HADS-D or HADS-A score ≥ 8) had 30% and 45%, respectively, higher odds of being current smokers; 19% and 37% higher odds of being obese and 31% and 24% higher odds of excessive alcohol consumption. Depressive patients had 34% higher odds of being non-adherent to their medication. At one-year follow-up, patients with depression (HADS-D score ≥ 11) had the highest attributable risk associated with mortality followed by: smoking, ischemic heart disease, anxiety, diabetes, hypertension chronic obstructive pulmonary disease and excessive alcohol consumption. Conclusion: Depression and anxiety in patients with cardiac disease is associated with cardiac risk behaviour such as smoking, obesity, excessive alcohol consumption and medication non-adherence. Depression and anxiety have an attributable risk associated with mortality that is comparable to other well-known risk factors such as smoking.