Abstract Introduction Heart failure (HF) is one of the major health problems in our environment today. Type 2 diabetes mellitus (DM2) is an important cardiovascular risk factor and can increase the burden of HF through various mechanisms. The incidence of HF in DM2 has not been well studied. Purpose The aim of our study was to evaluate the prevalence and incidence of HF in patients with DM2 followed in hospital cardiology and endocrinology departments. Methods The DIABET-IC study is a longitudinal cohort, prospective, multicenter follow-up study that included 1,249 consecutive patients with DM2 in 2018-2019 in 30 Spanish centers in cardiology and endocrinology outpatient clinics. HF was diagnosed according to the clinical records and following the criteria of the European Society of Cardiology. The prevalence of HF at the inclusion visit was analyzed, as well as the incidence of HF (new diagnoses) during a 3-year follow-up. Results Mean age was 67.3±+9.9 years, with 31.7% of the patients being women. Cardiology clinics included 61.9% of patients and endocrinology clinics the remaining 38.1%. There was a previous history of coronary artery disease in 38.6%, hypertensive heart disease in 21% and atrial fibrillation in 31.9%. Cardiovascular and antidiabetic drugs prescribed at the baseline and 3-year visits are shown in figure 1. Figure 2 summarizes the results of the study. The prevalence of HF at the baseline visit was 39.2%, 490 cases (with reduced LVEF 17.3%, mildly reduced 8.1% and preserved 13.8%). After a follow-up of 1,935/100 persons-year of cases without baseline HF, 58 incident cases of HF were diagnosed, 7.6% (32 in the first year, 13 in the second and 13 in the third year of follow-up). The incidence rate was 3.01/100 person-years (95%CI: 2.30-3.92). Of these 58 cases, 23.7% were with reduced LVEF, 28.9% with slightly reduced LVEF and 47.4% preserved. The incidence was higher in patients followed by endocrinology (3.90 vs 2.90/100 persons-year; p=0.042). At the end of the 3-year follow-up, including baseline prevalence, 46.8% of all patients had HF. Conclusions The prevalence and incidence of HF in patients with DM2 are very high. The incidence of HF is around 3% per year, which is almost 8 times higher than the rate found in large studies in the general population. Approximately half of the new cases were HF with preserved LVEF, and the other half with LVEF < 50%. The use of new antidiabetic drugs, such as iSGLT2, which have been shown to reduce the incidence of HF, should be encouraged.