Introduction: Muscular subpulmonic stenosis causing right ventricular outflow tract obstruction is an uncommon cardiac disease, especially when first diagnosed in adults. Diagnosis can be challenging when it is minimally symptomatic.

Case Presentation: We report a 40-year-old man who was referred to cardiology clinic for work-up of dyspnea and a heart murmur found on his physical examination. A transesophageal echocardiogram (TEE) revealed a muscular subpulmonic stenosis and a small perimembranous ventricular septal defect (VSD) with left-to-right shunt and severe right ventricular outflow tract obstruction (RVOT). Right heart catheterization showed an estimated gradient of 75 mmHg across the two chambers due to subpulmonary stenosis. The pressure in the proximal right ventricular chamber was 100/25 mmHg and 25/17 mmHg in the distal chamber. Surgical correction was successfully performed. A postoperative TEE showed no residual gradients across the RVOT.

Conclusions: Full echocardiographic examination of the right ventricle, including RVOT is essential for the diagnosis of this disease. Surgical correction appears to be a successful strategy for management of this rare condition in adults.