Abstract Body (Do not enter title and authors here): Background. Fluid resuscitation is recommended in patients with sepsis. Sepsis, however, may be associated with myocardial dysfunction. Additionally, myocardial dysfunction and insufficient cardiac reserves in patients with congestive heart failure (CHF) may complicate fluid resuscitation in the setting of sepsis. We aimed to determine whether CHF would affect fluid resuscitation in septic patients admitted to intensive care unit. Outcome of patients with and without CHF were compared. Methods. Unmatched and propensity score matched septic patients with or without CHF were examined in a retrospective cohort of critically ill adults from the MIMIC-IV database by multivariable logistic regression. Mortality and length of stay were compared. Generalized additive models were used for assessing association between fluid resuscitation and in-hospital mortality. Results. Of 24,376 critically ill patients with sepsis, 6838 (28.1%) were also diagnosed with CHF. CHF in septic patients was associated with higher in-hospital mortality with an adjusted odds ratios of 1.25 (95% confidence interval (CI)=1.14-1.37; p<0.001) in unmatched analysis. Compared with patients without CHF, those with CHF had higher in-hospital mortality (14.3% vs. 9.8%, p < 0.001) and received less IV fluid in the first 24 hours of ICU stay (median=1936 ml, IQR=808-3654 vs. 3037, IQR=1810-4585 ml, p<0.001). Similar results were obtained in propensity score matched septic patients with or without CHF. We also found that fluid resuscitation had a U-shaped association with in-hospital mortality with a lowest mortality at roughly 60 ml/kg in the first 24 hours of ICU stay in septic patients without CHF. In septic patients with CHF, liberal fluid resuscitation did not reduce mortality, while restrictive fluid resuscitation was associated with an increased mortality rate. Conclusions CHF was significantly associated with higher in-hospital mortality among septic patients. Adequate fluid resuscitation improved in-hospital mortality in septic patients without but not with CHF.