hypoplastic right heart syndrome (Monarch Disease Ontology id MONDO_0020291) can be described as follows. Hypoplastic right-heart syndrome (HRHS) is a rare, cyanotic congenital heart malformation caused by underdevelopment of the right-sided heart structures (tricuspid valve, RV, pulmonary valve, and pulmonary artery) commonly associated with an atrial septal defect, ostium secundum type. Pulmonary blood flow is diminished and right-to-left shunting occurs at the atrial level, leading to dyspnea, fatigue, atrial arrhythmias, right-sided heart failure, hypoxemia, repeated miscarriages that were mostly due to hypoxemia and cyanosis. Two subtypes of HRHS have been characterized: pulmonary atresia-intact ventricular septum and right ventricular hypoplasia. Also known as: right hypoplastic heart syndrome.