Background-To gain insight into the pathogenesis of right ventricular(RV) cardiomyopathy and ventricular tachycardia(VT), we determined the clinical and electroanatomic characteristics and outcome of ablative therapy in consecutive patients with(1) RV dilatation, (2) multiple left bundle-branch block(LBBB)-type VTs, and (3) an abnormal endocardial substrate defined by contiguous electrogram abnormalities. Methods and Results-All 21 patients had detailed RV bipolar electrogram voltage mapping. Eighteen patients had simultaneous left ventricular(LV) mapping, including all 4 patients with right bundle-branch block(RBBB) VT. VT was ablated in 19 patients by use of focal and/or linear lesions with irrigated-tip catheters in 10 of 19 patients. Eighteen patients were men, age 47±18 years, and none had a family history of RV dysplasia. RV volume was 223±89 cm3. Electrogram abnormalities extended from perivalvular tricuspid valves(5 patients), pulmonic valves (6 patients), or both valves (10 patients). Electrogram abnormalities always involved free wall, spared the apex, and included the septum in 15 patients (71%). The area of abnormality was 55±37 cm2 (range, 12 to 130 cm2) and represented 34±19%of the RV. In 52 of 66 LBBB VTs, the origin was from the RV perivalvular region. LV perivalvular low-voltage areas noted in 5 patientswere associated with a RBBB VT origin. No VT recurred after ablation in 17 patients(89%) during 27±22 months. Conclusions-In patients with RVcardiomyopathy and VT, (1) perivalvular electrogram abnormalities represent the commonly identified substrate and source of most VT, (2) LV perivalvular endocardial electrogram abnormalities and VT can occasionally be identified, and (3) aggressive ablative therapy provides long-term VT control. Background-To gain insight into the pathogenesis of right ventricular (RV) cardiomyopathy and ventricular tachycardia (VT), we determined the clinical and electroanatomic characteristics and outcome of ablative therapy in consecutive patients with (1) RV dilatation, (2) multiple left bundle -branch block (LBBB) -type VTs, and (3) an abnormal endocardial substrate defined by contiguous electrogram abnormalities. Methods and Results-All 21 patients with detailed RV bipolar electrogram voltage mapping. Eighteen patients had simultaneous left ventricular (LV) including all 4 patients with right bundle-branch block (RBBB) VT. VT was ablated in 19 patients by use of focal and / or linear lesions with irrigated-tip catheters in 10 of 19 patients. Eighteen patients were men, age 47 ± 18 years, and none had a family history of RV dysplasia. RV volume was 223 ± 89 cm3. Electrogram abnormalities extended from perivalvular tricuspid valves (5 patients), pulmonic valves (6 patients), or both valves The area of ​​abnormality was 55 ± 37 cm2 (range, 12 to 130 cm2) and represented 34 ± 19% of the patients The RV. In 52 of 66 LBBB VTs, the origin was from the RV perivalvular region. LV perivalvular low-voltage areas noted in 5 patients were associated with a RBBB VT origin. No VT recurred after ablation in 17 patients (89%) during 27 ± 22 months. Conclusions-In patients with RV cardiomyopathy and VT, (1) perivalvular electrogram abnormalities represent the commonly identified substrate and source of most VT, (2) LV perivalvular endocardial electrogram abnormalities and VT can occasionally be identified, and (3) aggressive ablative therapy provides long-term VT control.