BACKGROUND Focal atrial tachycardia (AT) originates from preferential sites, including the tricuspid and mitral annuli. AT arising from the atrioventricular annuli is initiated and terminated with programmed stimulation and is, in general, adenosine and verapamil sensitive. Para-Hisian AT arising from the apex of the triangle of Koch has been considered to be a distinct entity, characterized by unique electrophysiological properties. OBJECTIVE We sought to more fully delineate the electrophysiological and electrocardiographic properties of para-Hisian AT in a large series of patients. METHODS The study population consisted of 38 patients (63 ± 15 years; 23 female) with AT from the para-Hisian region. The ATs were focal and originated from the anteroseptal tricuspid annulus, in close proximity to the His bundle recording. Proximity to the His bundle was confirmed by electrogram recordings, fluoroscopy, and centrifugal activation during three-dimensional mapping. RESULTS The mean AT cycle length was 421 ± 69 ms. AT was associated with a distinct P-wave morphology that was significantly narrower than the P wave during sinus rhythm. Adenosine (5.0 ± 1.5 mg) terminated AT in 34/35 patients. Intravenous verapamil terminated AT in three of three patients. Catheter ablation was attempted in 30 patients and was successful in 26 (87%). CONCLUSIONS The para-Hisian region is a source of focal AT, with properties consistent with AT arising circumferentially along the tricuspid and mitral annuli, and should be considered a subset of this broader group of "annular" ATs. The electropharmacologic findings in para-Hisian AT are mechanistically consistent with cyclic AMP-mediated triggered activity.