Background: Brugada syndrome (BrS) is considered a purely electrical disease with variable electrical substrates. Variable rates of mechanical abnormalities have been also reported. Whether exists a link between electrical and mechanical abnormalities has never been previously explored. This investigational physiopathological study aimed to determine the relationship between the substrate size/location, as exposed by ajmaline provocation, and the severity of mechanical abnormalities, as assessed by cardiac magnetic resonance in patients with BrS. Methods: Twenty-four consecutive high-risk patients with BrS (mean age, 38±11 years, 17 males), presenting with malignant syncope and documented polymorphic ventricular tachycardia/ventricular fibrillation, and candidate to implantable cardioverter defibrillator implantation, underwent cardiac magnetic resonance and electroanatomic maps. During each examination, ajmaline test (1 mg/kg over 5 minutes) was performed. Cardiac magnetic resonance findings were compared with 24 age, sex, and body surface area-matched controls. In patients with BrS, the correlation between the electrical substrate extent and right ventricular regional mechanical abnormalities before/after ajmaline challenge was analyzed. Results: After ajmaline, patients with BrS showed a reduction of right ventricular (RV) ejection fraction ( P <0.001), associated with decreased transversal displacement (U, P <0.001) and longitudinal strain (ε, P <0.001) localized at RV outflow tract. In patients with BrS significant preajmaline/postajmaline changes of transversal displacement (ΔU, P <0.001) and longitudinal strain (Δε, P <0.001) were found. In the control group, no mechanical changes were observed after ajmaline. The electrical substrate consistently increased after ajmaline from 1.7±2.8 cm ² to 14.2±7.3 cm ² ( P <0.001), extending from the RV outflow tract to the neighboring segments of the RV anterior wall. Postajmaline RV ejection fraction inversely correlated with postajmaline substrate extent ( r =−0.830, P <0.001). In patients with BrS and normal controls, cardiac magnetic resonance detected neither myocardial fibrosis nor RV outflow tract morphological abnormalities. Conclusions: BrS is a dynamic RV electromechanical disease, where functional abnormalities correlate with the maximal extent of the substrate size. These findings open new lights on the physiopathology of the disease. Registration: URL: https://clinicaltrial.gov ; Unique identifier: NCT03524079.