Differentiation between the different right ventricular rhythm disorders and specifically between arrhythmogenic right ventricular dysplasia (ARVD) and right ventricular outflow tract (RVOT) tachycardias has important clinical implications but remains a clinical challenge. We tested the hypothesis that the spatial association of local electrographic parameters may be used to discriminate between these 2 entities. Electroanatomic mapping of the right ventricle was performed in 3 groups: patients who had typical RVOT tachycardia, a control group of patients who had no ventricular arrhythmias, and patients who had a diagnosis of ARVD based on clinical, electrocardiographic, and structural findings. Electroanatomic mapping in the RVOT tachycardia group showed normal electrographic parameters throughout the right ventricle (unipolar electrographic amplitude 9.9 ± 0.9 mV, duration 55 ± 1 ms, amplitude/duration 0.193 ± 0.022) that were no different from those in the control group. In contrast, dysplastic regions in the ARVD group were characterized by significantly lower amplitude (unipolar 3.6 ± 0.4 mV), prolonged electrographic duration (unipolar 73 ± 4 ms), and a decreased amplitude/duration ratio (unipolar 0.054 ± 0.008) compared with the unaffected zones in the same hearts and with all regions in the RVOT and control groups. Thus, endocardial electrographic parameters do not differ between patients who have RVOT and control patients. RVOT tachycardia can be differentiated from ARVD by the absence of abnormal right ventricular electrographic findings. This ability may have important clinical implications and supports the concept of different underlying mechanisms for these 2 entities.