Background Hypertrophic obstructive cardiomyopathy (HOCM) carries an increased risk for sudden cardiac death. No data regarding the percutaneous transseptal myocardial ablation (PTSMA) and epicardial left ventricular pacing (LVP)were reported.Methods Seven patients with recurrent symptoms and increased resting left ventricular outflow tract pressure gradient (LVOTG) after PTSMA and another 14 patients with HOCM without history of PTSMA were studied. Both resting and dobutamine stress echocardiography, PTSMA and LVP were routinely performed.Results In patients without previous PTSMA procedure, mild reduction of resting LVOTG was detected at 5 minutes after left ventricular pacing, and this reduction became significant at 10 minutes. All patients were divided into successful and unsuccessful groups according to their response to LVP. In contrary to patients in unsuccessful group, resting and R-S2 stimuli-induced LVOTG during PTSMA procedure were decreased dramatically ((9±5) mmHg vs (58±12) mmHg,(12±2) mmHg vs (113±27) mmHg, P＜0.001). Analysis of Logistic regression demonstrated that only LVOTG level during left ventricular pacing was an independent factor predicting the reduction of LVOTG immediately after PTSMA(odds ratio (OR), 0.59; 95% CI 2.67 to 5.82; P=0.0002).Conclusion Left ventricular endocardial temporary pacing plays a critical role in predicting acute effect on the reduction of LVOTG immediately after PTSMA procedure.