Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 12 1 2017 03 05 35 38 EN Reza Mollazadeh Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran. Masoud Eslami Imam Khomeini Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2017 02 11 2017 02 11 A 29-year-old woman was referred to our hospital due to exacerbation in dyspnea on exertion and easy fatigability. A known case of congenitally corrected transposition of the great vessels and congenital complete heart block, she had already received a permanent single-chamber pacemaker. Decision was made to implant a biventricular pacemaker for the treatment of the failing heart. Excellent coronary sinus lead implantation was done, conferring amelioration of symptoms, QRS narrowing in the electrocardiogram, and improvement of systemic ventricular systolic function in echocardiography. Over a 15-month follow-up period, she had no dyspnea on exertion. This case highlights the significance of upgrading pacemakers in patients with heart failure. https://rhythm.tums.ac.ir/index.php/jthc/article/view/677 https://rhythm.tums.ac.ir/index.php/jthc/article/download/677/501