Atrial tachyarrhythmias, including atrial fibrillation (AF) and atrial flutter, are common among patients with structural heart disease, and by extension patients with device implants.3- 5 The incidence of dual tachycardia among this population, defined as ventricular tachycardia (VT) or ventricular fibrillation that initiated in the setting of an ongoing atrial tachycardia or AF episode, is approximately 8.6%.3 Recognizing atrial arrhythmias, especially AF, is of paramount importance, given that the detection of AF in patients with ICDs is an independent predictor of mortality and can be a trigger for ventricular arrhythmias.3- 5 In addition, AF itself can result higher shock rates among patients with ICD implants.5- 7 Recognition is simpler in dual-chamber devices given the luxury of 2 channels being available. However, in cases where only a single-chamber channel is available, this can be challenging. Therefore, the surface ECG becomes the primary bedside tool the clinician can use for reaching an accurate diagnosis. In this case, the patient was initially determined correctly to have atrial flutter. However, recognizing the underlying AIVR via the surface ECG requires intricate knowledge of QRS morphology and AV dissociation, 2 clues that allow the clinician to reach an accurate diagnosis. The variability of the PR interval is another important aspect that proves the presence of AV dissociation.