The goal of this clinical trial is to learn if different types of heart rate control work to improve the clinical outcomes of patients with atrial fibrillation related to rheumatic mitral stenosis in terms of reducing hospitalizations, improving quality of life, and enhancing physical functional capacities. The two types of heart rate (HR) control are strict (resting HR of 60-80 bpm) versus lenient (resting HR of 81-110 bpm) rate control strategies. The main questions it aims to answer are: * Can lenient versus strict heart rate control reduce rehospitalization in patients with atrial fibrillation and rheumatic mitral stenosis? * Does lenient versus strict heart rate control improve the quality of life (QoL) in patients with atrial fibrillation and rheumatic mitral stenosis? * Does lenient versus strict heart rate control enhance functional capacity in patients with atrial fibrillation and rheumatic mitral stenosis? Researchers will compare strict rate control to lenient rate control to see if a particular rate control strategy is non-inferior to the other. Participants will: * Take standardized drugs as per PERKI (Indonesian Heart Association) guidelines for Atrial Fibrillation, which would be either beta-blockers, digoxin, or in combination. This standardized treatment of Atrial Fibrillation will be monitored once every month to see if the dose needs to be titrated in order to reach targeted heart rate control. * After the target of HR control is reached, the participant will be followed up every two weeks via telephone to check for any signs and symptoms. * Furthermore, after the HR target is reached, the participant will visit the cardiology outpatient clinics once every month for 3 consecutive months to see the clinical outcomes of hospitalization, QoL via SF-36 questionnaire, and functional capacities with 6MWT (6-minute walk test). * Additionally, the cardiac function would be evaluated by echocardiography at the baseline (time of enrollment) and at the end of the follow up period.