Echocardiography. 2018;1–4. wileyonlinelibrary.com/journal/echo | 1 © 2018 Wiley Periodicals, Inc. 1 | CASE PRESENTATION A 10-month-old male presented with persistent hypoxemia and oxy- gen requirement of 1.5 L throughout the day. He had a fetal diagnosis of large secundum atrial septal defect (ASD), pulmonary stenosis (PS), and mildly hypoplastic right ventricle (RV). Additionally, he had multi- ple comorbidities including tethered cord, bilateral chronic subdural hematomas status post ventriculo-peritoneal shunt placement, and laryngeal web status post multiple tracheal dilations. He had under- gone balloon pulmonary valvuloplasty at 4 months of age with re- portedly good result, despite which he continued to have persistent oxygen requirement. On clinical examination, he was cyanosed with oxygen saturations in the 80s, despite supplemental oxygen ther- apy. He had a normal cardiac examination without the presence of Received: 29 July 2018 | Revised: 10 September 2018 | Accepted: 27 September 2018 DOI: 10.1111/echo.14175 CASE REPORTS-PEDIATRIC Cor triatriatum dexter with right ventricular hypoplasia: Role of multimodality imaging in decision making Sruti Rao MD | Patcharapong Suntharos MD | Hani Najm MD | Rukmini Komarlu MD Cleveland Clinic Children’s Hospital, Cleveland, Ohio Correspondence Sruti Rao, Cleveland Clinic Children’s Hospital, Cleveland, OH. Email: raos@ccf.org Cor Triatriatum Dexter (CTD) is a rare congenital anomaly involving the systemic venous valves. Failure of regression of the right-sided sinus venosus valve leads to abnormal septation of the right atrium and a variety of right atrial and tricuspid valve obstructive lesions. The presentation can be varied ranging from asymptomatic to persistent neonatal cyanosis. We describe a late diagnosis of CTD in a 10-month-old male with persistent hypoxia despite balloon valvuloplasty for mild pulmonic valve stenosis with a large secundum atrial septal defect and a mildly hypoplastic right ventricle. KEYWORDS atrial septal defect, cardiac imaging, Cor triatriatum, pulmonary valve stenosis, right ventricular volume FIGURE 1 Transthoracic echocardiogram (TTE) subcostal long- axis view (2D and color compare) demonstrating a membrane in the supratricuspid region resulting in right-to- left shunting across the secundum ASD. ASD = atrial septal defect