BACKGROUND: Breast cancer patients are at risk of acute decompensated heart failure (ADHF) and protein-energy malnutrition (PEM) due to chemoradiation effects or cancer itself. There are no existing studies on the impact of PEM on breast cancer patients hospitalized for ADHF. This study aims to evaluate the effects of PEM on breast cancer patients admitted for ADHF. METHODS: Using the 2020 US National Inpatient Sample (NIS), our study analyzed breast cancer patients aged 18 and older. A multivariate logistic and linear regression analysis determined the odds ratio for various outcomes. The primary outcome was inpatient mortality among patients hospitalized for ADHF based on the presence or absence of PEM, while secondary outcomes included cardiogenic shock, anemia, and total hospital charges. RESULTS: Thirty thousand five hundred and fifty-five (30,555) patients were identified, predominantly female (99%) and Caucasian (71.4%). Among them, 6.07% were diagnosed with concurrent PEM. PEM was associated with higher in-hospital mortality risk (aOR 2.61), increased cardiogenic shock (aOR 3.17), anemia (aOR 1.43), more extended hospital stays (b 2.09), and higher hospital charges (average 8,285). CONCLUSIONS: The findings indicate that comorbid PEM is associated with increased risks of in-hospital mortality, anemia, cardiogenic shock, prolonged hospital stays and increased overall hospital costs among breast cancer patients admitted for ADHF.