Atrial fibrillation (AF) frequently occurs concurrently with heart failure (HF). The two conditions can exacerbate each other, resulting in higher morbidity and mortality. In our analysis, we evaluated mortality trends related to AF in individuals with underlying HF. Cross-sectional analyses were performed using publicly available data from the CDC database to compare AF-related age-adjusted mortality rates across age, gender, racial/ethnic, and geographic subgroups. Mortality trends were evaluated by fitting log-linear regression models followed by calculation of the average annual percentage change (AAPC) using the Monte Carlo permutation test. We identified a total of 55,917 deaths within the United States from AF with comorbid HF between 1999 and 2020. Males, older adults, White populations, and non-metropolitan regions had higher age-adjusted mortality compared to females, younger adults, Black populations, and metropolitan regions, respectively. The AAPC among younger adults was significantly higher compared to older adults. Our results demonstrate existing disparities among age, gender, racial, and geographic subgroups related to AF mortality among individuals with comorbid HF. Although decreased overall mortality was observed within younger populations compared to older populations, the prominent AAPC seen in younger populations warrants further investigation. Detection of AF among younger adults with comorbid HF should prompt intensification of preventative and treatment measures.