A 4mo male is brought to you for a well child check. No apparent abnormalities were noted at birth (APGARS 8 and 9), but you hear a II/VI holosystolic murmur. The mother denies any episodes of cyanosis or respiratory distress, but doesn’t think hes growing very well (birth wt. 2.7Kg, currently 5.6Kg). ECG shows evidence of left ventricular hypertrophy which is also supported by CXR. What is your diagnosis?