Background Alcohol septal ablation (ASA) decreases the left ventricular (LV) outflow gradient and relieves symptoms in patients with highly symptomatic hypertrophic obstructive cardiomyopathy (HOCM). The aim of this study was to evaluate the early course of hemodynamic, morphologic and clinical changes in younger and elderly patients. Methods and Results Forty-four consecutive patients (age, 24-81 years) underwent the ASA procedure for HOCM. Clinical and echocardiographic data were obtained at baseline and periodically up to 12 months after ASA. There was a significant correlation between septum thickness and age at baseline and in the early post procedural period (p=0.004 at baseline, p=0.0033 days postoperative, p=0.0193 weeks pos operative). The dependence of septal thickness on the duration of follow-up (p<0.001) was significantly influenced by age (p=0.026), which retained statistical significance after multivariate adjustment (p=0.031). A decrease in the gradient of the LV outflow was identified in all age-related groups of patients (p<0.001). After multivariate adjustment, there was a significant influence of age (p=0.003) and creatine kinase-MB peak (p=0.016) on the course of outflow gradient reduction. Conclusions ASA is an effective treatment option for patients with HOCM, irrespective of their age. Younger patients are characterized by a thicker basal septum at baseline and a slower hemodynamic improvement within the early post procedural period. (Circ J 2006; 70: 880 -884)