Objective To examine the association between mental health status after first-time myocardial infarction (MI) and new cardiovascular events or death, taking into account depression and anxiety as well as clinical, sociodemographic and behavioural risk factors.

Design Population-based cohort study based on questionnaires and nationwide registries. Mental health status was assessed 3 months after MI using the Mental Component Summary score from the Short-Form 12 V.2.

Setting Central Denmark Region.

Participants All patients hospitalised with first-time MI from 1 January 2009 through 31 December 2009 (n=880). The participants were categorised in quartiles according to the level of mental health status (first quartile=lowest mental health status).

Main outcome measures Composite endpoint of new cardiovascular events (MI, heart failure, stroke/transient ischaemic attack) and all-cause mortality.

Results During 1940 person-years of follow-up, 277 persons experienced a new cardiovascular event or died. The cumulative incidence following 3 years after MI increased consistently with decreasing mental health status and was 15% (95% CI 10.8% to 20.5%) for persons in the fourth quartile, 29.1% (23.5% to 35.6%) in the third quartile, 37.0% (30.9% to 43.9%) in the second quartile, and 47.5% (40.9% to 54.5%) in the first quartile. The HRs were high, even after adjustments for age, sociodemographic characteristics, cardiac disease severity, comorbidity, secondary prophylactic medication, smoking status, physical activity, depression and anxiety (HR_{3rd quartile} 1.90 (95% CI 1.23 to 2.93), HR_{2nd quartile} 2.14 (1.37 to 3.33), HR_{1st quartile} 2.23 (1.35 to 3.68) when using the fourth quartile as reference).

Conclusions Low mental health status following first-time MI was independently associated with an increased risk of new cardiovascular events or death. Further research is needed to disentangle the pathways that link mental health status following MI to prognosis and to identify interventions that can improve mental health status and prognosis.