Teaching electrophysiology is mostly about preparation, learning as much as possible about a tachycardia before delivering the energy source for ablation. This includes the history, the physical examination, careful review of the ECG and recorded tracings, and analysis and correct execution of maneuvers to identify tachycardia mechanisms accurately. However, at times the electrophysiologist learns while burning. Slowing or acceleration of an automatic tachycardia, decrease in electrogram amplitude, or evidence for collateral damage while ablating are all important to recognize. In this segment of Teaching Rounds in Electrophysiology, Kumar and Gehi1 discuss what we can learn when ablating reentrant arrhythmia based on changes noted in the tachycardia characteristics and activation sequence: a change in the cycle length of tachycardia without a change in the activation sequence, abrupt changes in the activation sequence but tachycardia continuing at the same rate, or occasionally changes in both rate and sequence despite the original tachycardia continuing. Article see p e68 While burning, when the tachycardia cycle length stays exactly the same, likely the same tachycardia continues, but why would there be an abrupt change in the activation sequence?