BackgroundA patient’s knowledge of heart failure (HF) is associated with better outcomes. The more information patients have about their illness, the less likely they are to be readmitted to the hospital. Such knowledge includes the cause, symptoms, probable duration, and expected evolution of the clinical picture. In Portugal, a tool for testing patient knowledge is an unmet need. Therefore, this study aimed to adapt and test the Chronic Heart Failure Knowledge Questionnaire (KQCHF) for the Portuguese context.MethodsThis work includes three cross-sectional studies. In Study 1, subjects were divided between before and after receiving information about HF. In Study 2, participants answered the questionnaire before and after reading the brochure. In Study 3, KQCHF was applied to patients with HF. Studies 1 and 2 were carried out in the general population. Study 3 was carried out with HF outpatients. Convenience sampling was applied to participants in the three studies.ResultsIn Study 1 (n= 45), those who received information had better scores (9.2 ± 1.9) than those who did not (6.0 ± 2.3). In Study 2 (n= 21), the scores were higher after reading the brochure (10.4 ± 1.7 vs. 6.5 ± 2.9). In Study 3 (n= 169), women had better scores than men (9.1 ± 2.1 vs. 8.3 ± 2.2, overall: 8.5 ± 2.2), and knowledge was correlated with education (r= .340,p< .001) and age (r= -.170,p= .030).ConclusionThe Portuguese adaptation of KQCHF captured relevant knowledge about HF and has shown promising results for clinical and research purposes. The questionnaire can be useful in assessing HF patients’ knowledge of their disease and as a basis for the implementation of general and personalised educational strategies to improve HF knowledge and, therefore, promote health literacy and self-care.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12872-023-03325-5.