1. The purpose of the present study was to explore the relationship between electrocardiogram (ECG) patterns of right ventricular outflow tract (RVOT) premature ventricular contractions and the three-dimensional distribution of the target sites. 2. Thirty-three consecutive patients were included in the study. The target sites were identified by non-contact mapping and confirmed by successful ablation. The distribution of the target sites in the three-dimensional reconstructed geometry of the RVOT was classified in three directions: (i) anterior (A)/posterior (P); (ii) free wall (F)/septal (Se); and (iii) superior (Su)/inferior (I). The ECG characteristics were then analysed according to the three-dimensional distribution of the target sites. 3. The following indices were helpful to identify the position of the target site: (i) QRS duration (> or = 150 msec = F; < 150 msec = Se; P < 0.05); (ii) the R wave pattern in the inferior leads (RR' or Rr' = F; R = Se; P < 0.05); (iii) the R wave amplitude in the inferior leads (high = Se; low = F; P < 0.05); (iv) the initial r wave width in lead V(1) (wide = F; narrow = Se; P < 0.05); (v) the QS wave amplitude in aVR and aVL (if aVR < aVL, A; if aVR > or = aVL, P; P < 0.05); and (vi) the initial r wave amplitude in lead V(1) and V(2) (if V(1) > or = 0.15 mV and V(2) > or = 0.3 mV, Su; if V(1) < 0.15 mV or V(2) < 0.3 mV, I; P < 0.05). 4. In conclusion, the ECG characteristics were associated with target site locations in all three directions.