Tehran University of Medical Sciences The Research in Heart Yield and Translational Medicine (RHYTHM) 3115-7270 7 1 2012 01 15 30 32 Mohammad Assadian Rad Heshmat Cardiovascular Medical Center, Guilan University of Medical Sciences, Rasht, Iran. Zahra Emkanjoo Heshmat Cardiovascular Medical Center, Guilan University of Medical Sciences, Rasht, Iran. Hassan Moladoust Heshmat Cardiovascular Medical Center, Guilan University of Medical Sciences, Rasht, Iran. 2015 10 03 T-wave oversensing occurs when the counter starts giving dual beeps for every cardiac cycle instead of one. This usually happens when the monitoring lead displays a tall T wave, which is also sharp. R wave sensing algorithms of the devices do not sense T wave because the slow rate of the T wave is much less than that of the R wave. But the slow rate of T waves may change with time and also because of parameters like potassium levels and hyperglycemia. We present a 67-year-old female who underwent the implantation of cardiac resynchronization therapy (cardiac resynchronization and implantable cardioverter defibrilator [CRT-D]) because of severe left ventricular systolic dysfunction and ventricular dyssynchrony experienced recurrent inappropriate implantable cardioverter-defibrillator (ICD) shocks and CRT failure. Device analysis showed that the CRT failure was in consequence of T-wave oversensing due to hyperglycemia. Elimination of the T-wave oversensing after hyperglycemia control conferred  good biventricular pacing and good response to CRT  during a 6-month follow-up period. https://rhythm.tums.ac.ir/index.php/jthc/article/view/238 https://rhythm.tums.ac.ir/index.php/jthc/article/download/238/236