Background: Heart failure (HF) is a common clinical syndrome, particularly in older people, and symptoms can develop gradually. The aim of this study was to explore the role of informal carers in the HF diagnostic process.; Methods: Secondary analysis of qualitative interviews with 16 participants with a new diagnosis of HF. Original interviews were conducted in the participant's home, with carers present in some cases. Interview transcripts were re-analysed using the Framework Method for themes pertaining to informal carers and how they were involved in the diagnostic process.; Results: Informal carers often noticed symptoms, such as breathlessness, before participants. In some cases, carers colluded with participants in normalising symptoms but over time, when symptoms failed to resolve or got worse, they encouraged participants to seek medical help. Adult children of participants commonly initiated help-seeking behaviour. During the diagnostic process, carers coordinated participants' healthcare through advocacy and organisation. Carers were keen to be informed about the diagnosis, but both participants and carers struggled to understand some aspects of the term 'heart failure'.; Conclusions: Carers play a crucial role in HF diagnosis, particularly in initiating contact with healthcare services, and should be empowered to encourage people with HF symptoms to seek medical help. Improving public awareness of HF could mean informal carers are more likely to notice symptoms. The important role of carers in supporting the patient's route to diagnosis should be incorporated into future care pathways and explored in further research.