Cardiac resynchronization therapy (CRT) improves left ventricular function, especially in patients with left bundle branch block or those receiving chronic right ventricular pacing. CRT is typically accomplished by placing a right ventricular endocardial pacing lead and a left ventricular pacing lead via the coronary sinus to a coronary vein overlying the lateral or posterolateral left ventricle. CRT can be combined with an implantable defibrillator or with a pacemaker. Limited data are available to compare these two versions of CRT head to head. This review summarizes the relevant trials and meta-analyses regarding these two forms of CRT.