Background: Nutritional status, characterised by body mass index (BMI), may influence therapeutic decisions in heart failure with preserved ejection fraction (HFpEF). The objectives of this study were to identify clinical and echocardiographic characteristics associated with nutritional status and to analyse therapeutic strategies in HFpEF patients in Argentina. Materials and Methods: This prospective, multicentre observational registry enrolled outpatients or those discharged from hospitals, with prior informed consent. The study spanned from December 2022 to February 2024. Inclusion criteria were: 1) presence of current signs and symptoms, LVEF ≥50%, 2) structural heart disease with LVH, LAE, or average E/e’ ≥15 on Doppler, 3) elevated natriuretic peptides: sinus rhythm: NTproBNP >125 pg/ml or BNP >35 pg/ml; Atrial fibrillation/flutter: NTproBNP >375 pg/ml or BNP >105 pg/ml; and 5) commitment to 6-month and 1-year follow-ups. Exclusion criteria comprised: 1) acute coronary syndrome, 2) coronary artery bypass grafting, or valve replacement within the preceding 3 months, 3) confirmed infiltrative or hypertrophic cardiomyopathy, severe valvular disease, 4) severe illness with <1-year prognosis, and chronic renal failure on permanent dialysis. Results: A total of 449 patients were enrolled, with 440 having available BMI data for this analysis. Patient enrolment was consistent across centres and nationwide. BMI analysis revealed 0.7% undernutrition, 16.6% normal weight, 32% overweight, and 50.7% obesity. In Figure1 showed the analysis of clinical, laboratory, echocardiographic, and HF severity variables according to BMI. Significant differences were found in treatment, with lower use of RAS inhibitors and beta-blockers in non-normal weight patients compared to those with overweight and obesity. Conclusions: For a similar HFpEF severity profile, the phenotype according to BMI suggests different clinical characteristics. Underweight/normal weight patients were older, with more LAE and pulmonary hypertension, and fewer risk factors. Obesity was present in half of the cases, characterised by younger patients with a high burden of cardiovascular risk factors. This impacts the use of certain heart failure medications.