Background: Heart failure (HF) diagnosis as reported in primary care medical records is not always properly confirmed and could result in over-registration.Objectives: To determine the proportion of registered HF that can be confirmed with information from primary care medical records and to analyse related factors.Methods: A cross-sectional study. The medical records of 595 HF patients attended in two primary healthcare centres in Barcelona (Spain) were revised and validated by a team of experts who classified diagnosis into confirmed, unconfirmed, and misdiagnosis. Variables potentially related to the confirmation of the diagnosis were analysed. The revision of medical records and data collection took place from 15 January to 31 March 2014.Results: Mean (standard deviation) age was 78 (10) years and 58% were women. The diagnosis could be confirmed in 53.6% of patients. Factors associated with a greater probability of having a confirmed diagnosis were age (yearly OR: 0.97, 95%CI: 0.95–0.99), cardiologist follow-up (OR: 3.66, 95%CI: 2.46–5.48), history of ischaemic heart disease (OR: 2.18, 95%CI: 1.36–2.48), atrial fibrillation (OR: 2.01, 95%CI: 1.34–3.03), and prescription of loop diuretics (OR: 3.24, 95%CI: 2.14–4.89).Conclusion: Only in half of the patients labelled as HF in primary care medical records could this diagnosis be further confirmed. Variables regularly registered in clinical practice could help general practitioners identify those patients requiring a revision of their HF diagnosis.