Aims: Systematic screening for anxiety and depression is widely recommended as a core component of cardiac rehabilitation in ischemic heart disease, however, recommendation-practice gaps are common and limited knowledge exists about factors hindering and supporting implementation. The study aimed to assess adherence to national clinical guideline recommendations and to gain a greater understanding of the implementation of screening in real-world practice. Methods: An observational, longitudinal mixed-methods design including hospitals and municipalities in Denmark. We retrieved nationwide survey data from 2013, 2015, 2018 and 2021 to assess adherence to screening on programme level, and clinical quality registry data from 2016 to 2020 to assess proportion of patients screened. Data were analysed descriptively. Semi-structured interviews with healthcare professionals were conducted in 2015 (n = 11) and 2020 (n = 11) to explore how screening was conducted and factors supporting implementation. Normalization Process Theory guided interviews and content analysis. Results: Screening on programme level increased from 61% to 88% in hospitals and 20% to 89% in municipalities. The individual proportion of patients screened remained relatively stable in both hospitals and municipalities overall, however with considerable inter-site differences. Screening practices became more aligned to guidelines, pushed by formal recommendations and monitoring, and pulled by activities strengthening the knowledge and motivation among staff. Conclusion: Screening for anxiety and depression improved considerably over the seven-year period, from a scattered practice driven by individuals to a movement where healthcare professionals had a feeling of going with the flow. Nationwide implementation of screening requires national and local supporting activities and a continuous effort.