Introduction: The aim of this study was to evaluate the effect of different temperatures of sodium hypochlorite (NaOCl) on the cyclic fatigue resistance of the heat treated file systems. Methods: The cyclic fatigue resistance of Reciproc 25 (VDW Dental, Munich, Germany), Reciproc Blue R25 (VDW), WaveOne Primary (Dentsply Maillefer, Ballaigues, Switzerland), WaveOne Gold Primary (Dentsply Maillefer), and One Shape (25.06; Micro Mega, Besancon, France) was tested in the following conditions: control (no immersion), immersion in distilled water (DW) at 37 degrees C +/- 1 degrees C, immersion in DW at 60 degrees C +/- 1 degrees C, immersion in NaOCl at 37 degrees C +/- 1 degrees C, and immersion in NaOCl at 60 degrees C +/- 1 degrees C. The immersion period was 5 minutes for all conditions. A stainless steel artificial canal with a curvature of 60 and a 5-mm radius was used. The time to failure and fragment lengths were recorded for each instrument, and data were subjected to statistical analysis. Results: Reciproc Blue showed greater cyclic fatigue resistance in all conditions compared with the other systems (P <.05). Immersion in NaOCl at 60 degrees C negatively affected all instruments' cyclic fatigue resistance except Reciproc Blue. Immersion in DW at 60 degrees C increased the cyclic fatigue resistance of Reciproc Blue. Heat-treated files presented higher fatigue resistance than traditional files. Conclusions: A high temperature of NaOCl affected the cyclic fatigue life of the file systems. Instruments produced with heat treatment presented a longer fatigue life.