oonan syndrome is one of the most common nonchromosomal syndromes frequently accompanied by cardiovascular malformations. 1 The major cardiovascular defects are valvular pulmonary stenosis, commonly due to a dysplastic valve, 2,3 and hypertrophic cardiomyopathy (HCM), which predominantly affects the interventricular septum and left ventricle. [4][5][6][7][8][9] We report an adult case of Noonan syndrome with biventricular HCM accompanied by isolated right ventricular outflow tract (RVOT) obstruction without valvular abnormalities. To the best of our knowledge, these conditions are regarded as rather uncommon manifestations of cardiac defects in adults with Noonan syndrome. Case ReportA 42-year-old man with dyspnea and palpitation on exertion was referred from his local hospital for further cardiac examination in April 2000. Heart murmur and electrocardiographic abnormalities were first noticed when he was 10 years of age, and he had experienced mild dyspnea on exertion since that time. On admission, blood pressure was 118/68 mmHg and pulse was regular at 72 beats/min. Neither mental retardation nor sexual infantilism was observed. He was of short stature (152cm; < mean -3.0 SD), had a short neck, a shield-like chest with widely spaced nipples, cubitus valgus (Fig 1A), and the characteristic facial traits of ocular hypertelorism and low-set posteriorly rotated ears ( Fig 1B). A grade 3 systolic ejection murmur was heard at the mid-left sternal border and S4 was heard at the apex. An electrocardiogram showed left axis deviation, P waves with high peaks in the inferior limb leads, and deep S waves over the precordial leads. Chest X-ray showed cardiomegaly with normal pulmonary vascularity. Laboratory tests revealed prolongation of the activated partial thromboplastin time (46.2 s; normal value, 24-37 s) and a somewhat deficient clotting factor 11 (61.2%; normal value, 75-137%) but without any hepatic dysfunction. The lymphocyte karyotype showed a normal male pattern.Transthoracic echocardiography (Fig 2) revealed biventricular hypertrophy with asymmetric septal hypertrophy. The hypertrophied septum bulged out into the outflow portion of the right ventricle, thus reducing the size of the right ventricular cavity and resulting in outflow obstruction. Transesophageal echocardiography (Fig 3) demonstrated far more pronounced hypertrophy in the interventricular septum than in the free wall of each ventricle and marked narrowing of the RVOT. The pulmonary valve was normal. Magnetic resonance imaging clearly demonstrated marked biventricular hypertrophy including that of the left ventricular free wall (Fig 4). Cardiac catheterization showed a pulmonary capillary wedge pressure of 11 mmHg, pulmonary arterial pressure of 22/12 (16) mmHg, RVOT pressure of 22/6 mmHg, right ventricle apex pressure of 70/6 mmHg, right atrial pressure of 6 mmHg, systemic arterial pressure of 110/70 (90) mmHg, and cardiac index of 1.44 L·min -1 · m -2 . A systolic pressure gradient of 48 mmHg was seen across the right ventricular outflow tract (F...