Atrial fibrillation (AF) is the most common form of irregular heart rhythm increasing the risk of death or disability. This rhythm disturbance is common among patients with rheumatic heart disease. Along with clinical manifestations of heart valve defect, AF additionally aggravates the course of the underlying disease. To date, on-pump surgeries have reached a new level of development. Appropriate surgical experience and improvement of myocardial protection reduced surgery time and improved postoperative outcomes. We present successful surgical treatment of a patient with severe mitral stenosis and long-term persistent AF who underwent a modified method of radiofrequency left atrial ablation (patent for invention No. 2758133 dated 10/26/2021) under warm blood cardioplegia.