We report a case of acute left ventricular failure at one hour after transcatheter closure of a secundum atrial septal defect (ASD) in a 28-year-old man with hypertrophic cardiomyopathy. Afforded noninvasive mechanical ventilation and the administration of intravenous morphine and high doses of furosemide, the patient exhibited improvement of his clinical condition, redtion of pulmonary congestion at chest X-ray, and satisfactory blood gas analyses in twelve hours. Twentyfour hours later, the patient received oral administration of furosemide and metoprolol. After 7 days the patient was discharged in good clinical condition. At follow-up at 12 months, the patient had remained symptomatically improved from NYHA Class Ⅲ symptoms before the procedure to Class Ⅱ symptoms. There was no latent arrhythmia at the follow-up examination. Follow-up transthoracic echocardiography estimated an improvement of the left ventricular function. So,transcatheter closure of a secundum ASD in a patient with hypertrophic cardiomyopathy is feasible, and a thorough understanding of the hemodynamic condition of ASD and hypertrophic cardiomyopathy will reduce the complication of ASD closure.