Radiofrequency (RF) refers to the portion of the electromagnetic spectrum in which electromagnetic waves can be generated by feeding an alternating current to an antenna. RF energy is electrically conducted, not radiated, during catheter ablation, and RF rarely induces rapid polymorphic arrhythmias. When using RF to measure lesion size in a steady state, the lesion size is proportional to the temperature measured at the tissue-electrode interface and the RF power amplitude. Focal ablation using RF is the treatment of choice for all supraventricular tachyarrhythmias, including AV nodal reentry, tachycardias with concealed accessory pathways, incessant automatic atrial tachycardia, isthmus dependent atrial flutter, and other macroreentrant atrial tachycardias. The isolation of pulmonary veins by RF energy has been successful for paroxysmal atrial fibrillation. (Korean J Med 2016;90:206-209)