Background <p>Rate control is a primary treatment approach for managing atrial fibrillation (AF). However, a unified standard for the optimal level of control remains unestablished. This study aimed to investigate the impact of strict versus lenient heart rate control strategies on exercise capacity in patients with AF by assessing cardiopulmonary exercise test (CPET) results.</p> Methods <p>A total of 693 patients with AF were included in this study. The patients were categorized into three groups on the basis of their resting heart rate: strict rate control (resting heart rate &lt; 80 beats per minute and heart rate during moderate exercise &lt; 110 beats per minute), lenient rate control (resting heart rate &lt; 110 beats per minute), and uncontrolled rate (resting heart rate ≥ 110 beats per minute. CPET indicators were compared across the different rate control strategies, and trend analyses were conducted to explore whether there was a correlation between heart rate control and exercise capacity.</p> Results <p>Significant differences in the maximum load, respiratory exchange ratio (RER), peak oxygen uptake (peak VO₂), peak oxygen pulse, and ventilatory equivalent (VE/VCO₂) at the anaerobic threshold were detected among the groups in the strict control, lenient control, and uncontrolled groups (all <i>p</i> &lt; 0,05). However, no significant differences were detected in the anaerobic threshold or ventilation parameters among these groups. Trend analyses indicated that stricter heart rate control was associated with significant increases in maximum workload, peak VO₂, peak oxygen pulse, and ventilatory equivalent.</p> Conclusion <p>In patients with AF, strict heart rate control may enhance exercise capacity, suggesting the importance of effective heart rate management strategies.</p>