For all groups, data for body-surface potential mapping (BSPM) will be recorded during induced VT (Group A& B), pacing from virtual VT exit sites which are several points selected around the scar margin to represent the VT exit site (group C) or index pacing site which is a pacing site selected as a reference in the RV of patients presented with SVT (group D) and from different pacemapping sites including successful and unsuccessful ablation sites if applicable. All data will be imported into customized software.