Abstract OBJECTIVES The purpose of this study was to compare the treatment effects of septal myectomy with dual-chamber pacing in patients with hypertrophic obstructive cardiomyopathy (HOCM). BACKGROUND The optimal treatment for symptomatic patients with drug-refractory HOCM is unknown. Both dual-chamber pacing and surgical myectomy may result in subjective symptom improvement. However, no direct comparisons with objective end points have been reported. METHODS Thirty-nine patients with symptomatic HOCM were analyzed in this concurrent cohort study. Twenty patients underwent surgical myectomy, and 19 received dual-chamber pacemakers based on patient preference. These patients had prospective baseline and follow-up evaluations including physician assessment, echocardiography and standardized metabolic treadmill exercise testing. RESULTS Baseline symptom status, left ventricular outflow tract gradients, exercise times and maximal oxygen consumption peak were similar between the two groups. Left ventricular outflow gradient was reduced from 76 ± 57 to 9 ± 17 mm Hg (p = 0.0001) after myectomy, and from 77 ± 61 to 55 ± 39 mm Hg (p = 0.07) after pacing (p = 0.02 for comparison with myectomy). Ninety percent of myectomy patients experienced symptomatic improvement as compared with 47% in the pacing group. Exercise duration increased significantly from 6.6 ± 2.8 to 8.7 ± 3.0 min (p = 0.0003) after myectomy compared with a change from 6.4 ± 2.1 to 7.0 ± 2.2 min (p = NS) in the pacing group. Maximal oxygen consumption increased from 19.4 ± 6.4 to 22.2 ± 6.5 ml/kg/min after myectomy (p = 0.004), whereas the pacing group did not experience any significant change (19.6 ± 6.5 vs. 20.1 ± 6.5 ml/kg/min, p = NS). CONCLUSIONS Surgical myectomy and dual-chamber pacing improve subjective measures of functional status in patients with symptomatic HOCM. In this nonrandomized study, myectomy offered greater reduction in left ventricular outflow tract gradients and larger improvements in objective measures of patient symptoms and functional status when compared with dual-chamber pacing.