Abstract Aim Classic Morrow septal myectomy for hypertrophic obstructive cardiomyopathy(HOCM) sometimes employ contemporary modifications to widen and extend resection forimproved left ventricle (LV) reconstruction.Outcomes of classic and modified Morrow septalmyectomy were compared in HOCM patients.Methods A retrospectivestudy was conducted of HOCM patients treated with classic ormodified Morrow septal myectomy from January 2005 to July 2011 at one facility.Preandpost-operative ventricular septal thickness, LV outflow tract velocity and gradient weremeasured echocardiographically.Results Ventricular septal thickness was significantly decreased in both modified and classicoperation groups (25.04±7.05 to 18.38±6.55 mm; 23.10±3.64 and 17.38±4.39 mm), LVoutflow tract velocity (414.83±83.33 to 159.72±60.84 mm/s; 433.08±101.68 to248.46±101.88 mn/s) and gradient (77.94±29.16 to 17.56±9.39 mmHg; 78.45±40.16 to34.29±21.52 mmHg).Notably, change in LV outflow tract gradient and velocity weresignificantly larger in the modified Morrow group than in the classic Morrow group.In theclassic group, 14 (87.5%) patients fully recovered and 2 exhibited LV outflow velocities of 411 mm/s with severe LV outflow obstruction after surgery.All patients in modified group fully recovered.Conclusions LV outflow tract gradient and velocity were minimized following modifiedMorrow septal myectomy, indicating better overall restoration of normal cardiac flow inHOCM patients.