The goal of this observational study is to report the outcomes after septal myectomy in young children and infants and identify the mechanisms of residual or recurrent obstruction after surgery. in The main question[s] it aims to answer are:

• What is the early and mid-term results of septal myectomy in young children and infants with severe and extensive obstructive hypertrophic cardiomyopathy (HCM)?
• What are the mechanisms of residual or recurrent obstruction?

Echocardiography and clinical course of children and infants under the age of 14 who underwent septal myectomy for hypertrophic obstructive cardiomyopathy from January 2013 to December 2020 will be followed up.

Inclusion Criteria:

• Clinical diagnosis of hypertrophic obstructive cardiomyopathy (HOCM)
• Age young than 14 years
• Patients who have undergone septal myectomy

Exclusion Criteria:

• older than 14 years old;
• secondary left ventricular hypertrophy (LVH) related to subaortic stenosis or aortic stenosis.

Children with HOCM who remain severely symptomatic despite medical therapy or have a particularly high resting LVOT gradients (>100mmHg) underwent septal myectomy by the same surgeon Y from January 2013 to December 2020. A total of 56 consecutive children younger than 14 were included. All patients were on Beta blockers therapy and symptomatic.