Background and Objectives: Previous studies suggest a potential link between dietary fiber intake and the prevalence of heart failure (HF) among the general population. However, the specifics of this relationship among those with cardiovascular conditions remain less explored. This study aims to examine the correlation between dietary fiber intake and HF among patients with a history of cardiovascular diseases, integrating physical activity levels to provide a broader perspective on lifestyle impacts. Methods: This cross-sectional study included non-pregnant individuals aged ≥20 years from the NHANES database. Dietary fiber intake was assessed through two 24-hour dietary recalls, and HF status was determined via questionnaires. Physical activity levels were quantified using MET-minutes/week based on responses in NHANES. Demographic characteristics and comparisons between groups were analyzed using SPSS software, and logistic regression was applied to assess the impact of dietary fiber and physical activity on HF outcomes. Results: A total of 17,534 participants with a history of cardiovascular conditions were evaluated, classified into HF (n = 1,268) and non-HF (n = 16,266) groups. HF participants had significantly lower dietary fiber intake (12.59±8.39 g/day) compared to the non-HF group (13.51±8.51 g/day, p=0.010). Individuals with dietary fiber intake below 12.45 g/day exhibited a higher incidence rate of HF (53.7% vs. 49.4%, p=0.038). Additionally, the HF incidence was higher among participants with minimal physical activity (8.3% vs. 5.8%, p=0.021). Participants engaging in moderate to high levels of physical activity with adequate fiber intake demonstrated the lowest odds of HF (odds ratio <0.716). Conclusions: The findings from NHANES data suggest that among those with cardiovascular conditions, both higher dietary fiber intake and increased physical activity levels are associated with reduced odds of developing HF. This study underscores the importance of a multifaceted lifestyle approach in managing heart health within this vulnerable population.