The integration of transvenous left ventricular pacing to a conventional pacemaker (cardiac resynchronization pacemaker, CRT-P) or an implantable cardioverter defibrillator (CRT-D) has offered effective alternative therapy for patients with heart failure. Novel CRT-D algorithms have improved the ways in which common problems encountered in heart failure patients can be addressed and effectively managed. However, this comes at the expense of increasingly complex device function and, therefore, troubleshooting. Here, a systematic approach to addressing CRT-D malfunction, including pacing/sensing malfunction, loss of synchronization, and generator malfunction, is discussed.