We describe the case of a 23-year-old girl with unknown HCM, that has syncope after a basketball game. In the medical evaluation Cardiac auscultation in left lateral decubitus and orthostatic position revealed no systolic murmur, and she did an echocardiogram that reveals HCM. She has septal hypertrophy (Figure 1 and see VIDEO 1 in Supplementary Material available online at doi10.5402/2011/346797), and she does not have systolic anterior movement of mitral valve (SAM) or intraventricular gradient (VIDEO 1 and VIDEO 2). 
Treadmill exercise echocardiogram was performed, using the standard Bruce protocol, and the patient did not develop LVOT gradient at peak exercise (Figure 2). 
After finishing the exercise we maintained the patient in orthostatic position and SAM of mitral valve and LVOT gradient greater than 100 mmHg (Figure 3 and VIDEO 3) developed. With evidence of falling systolic arterial pressure from 130 to 110 mmHg in that moment we put the girl in supine position. Previously considered a nonobstructive HCM, after the exercise echocardiography, the patient was considered to have an obstructive pattern with probable influence in clinical symptoms. Therefore, she was medicated with bisoprolol 5 mg a day.