AbstractIntroductionChemical ablation by retrograde infusion of ethanol into the vein of Marshall (VOM‐EI) can facilitate the achievement of mitral isthmus block. This study sought to describe the efficacy and safety of this technique.Methods and ResultsTwenty‐two consecutive patients (14 males, median age 71 years) with attempted VOM‐EI for mitral isthmus ablation were included in the study. VOM‐EI was successfully performed with a median of 4 ml of 96% ethanol in 19 patients (86%) and the mitral isthmus was successfully blocked in all (100%). Touch up endocardial and/or epicardial ablation after VOM‐EI was necessary for 12 patients (63%). Perimitral flutter was present in 12 patients (63%) during VOM‐EI and terminated or slowed by VOM‐EI in 4 and 3 patients, respectively. The low‐voltage area of the mitral isthmus region increased from 3.1 cm² (interquartile range [IQR] 0–7.9) before to 13.2 cm² (IQR: 8.2–15.0) after VOM‐EI and correlated significantly with the volume of ethanol injected (p = .03). Median high‐sensitive cardiac troponin‐T increased significantly from 330 ng/L (IQR: 221–516) the evening of the procedure to 598 ng/L (IQR: 382–769; p = .02) the following morning. A small pericardial effusion occurred in three patients (16%), mild pericarditis in one (5%), and uneventful VOM dissection in two (11%). After a median follow‐up of 3.5 months (IQR: 3.0–11.0), 10 of 18 patients (56%) with VOM‐EI and available follow‐up had arrhythmia recurrence. Repeat ablation was performed in five patients (50%) and peri‐mitral flutter diagnosed in three (60%).ConclusionVOM‐EI is feasible, safe, and effective to achieve acute mitral isthmus block.