Autonomic dysfunction may occur as a consequence of radiofrequency (RF) catheter ablation of a variety of supraventricular tachycardias. Effects suggestive of autonomic dysfunction that may be seen acutely during the ablation procedure include sudden profound slowing of the sinus rate or transient AV block. These abnormalities may occur during application of RF current, typically along the tricuspid or mitral annulus, at sites distant from both the sinus and AV nodes; they resolve quickly when RF current delivery is terminated. The most common long-term indication of autonomic dysfunction after ablation is inappropriate sinus tachycardia. This complication, rarely a lasting significant clinical problem, is seen after AV node modification and after ablation of accessory pathways. It usually resolves within several months. The mechanism appears to be loss of parasympathetic influence on the sinus node. Autonomic dysfunction after ablation of ventricular tachycardia has not yet been described, but could occur as newer catheter technologies capable of producing larger lesions are perfected.