A 4-year-old boy with Noonan syndrome accompanied by hypertrophic obstructive cardiomyopathy presented with refractory heart failure owing to severe left ventricular outflow obstruction and mitral regurgitation. He underwent mitral valve replacement and trans-mitral myectomy. The pathology of the resected myocardium was consistent with hypertrophic cardiomyopathy, and the mitral valve leaflets were severely degenerated. Compared with a control patient who is a non-syndromic 4-year-old boy with hypertrophic obstructive cardiomyopathy, mitral pathology was much more severe in Noonan syndrome. Regarding trans-mitral myectomy, residual pressure gradient at the mid-ventricular level made us think about more aggressive muscle resection with various approaches.
