<unk>  (or triatrial heart) is a congenital heart defect where the left atrium<unk>  sinistrum) or right atrium<unk>  dextrum) is subdivided by a thin membrane, resulting in three atrial chambers (hence the name).<unk>  represents 0.1% of all congenital cardiac malformations and may be associated with other cardiac defects in as many as 50% of cases. The membrane may be complete or may contain one or more fenestrations of varying size.<unk>  triatrium sinistrum is more common. In this defect there is typically a proximal chamber that receives the pulmonic veins and a distal (true) chamber located more anteriorly where it empties into the mitral valve. The membrane that separates the atrium into two parts varies significantly in size and shape. It may appear similar to a diaphragm or be funnel-shaped, bandlike, entirely intact (imperforate) or contain one or more openings (fenestrations) ranging from small, restrictive-type to large and widely open. In the pediatric population, this anomaly may be associated with major congenital cardiac lesions such as tetralogy of Fallot, double outlet right ventricle, coarctation of the aorta, partial anomalous pulmonary venous connection, persistent left superior vena cava with unroofed<unk> onary sinus, ventricular septal defect, atrioventricular septal (endocardial cushion) defect, and common atrioventricular canal. Rarely, asplenia or polysplenia has been reported in these patients. In the adult,<unk>  is frequently an isolated finding.
Cor triatriatum
Phidippides cardiomyopathy
Algor mortis
Crisscross heart
Libman–Sacks endocarditis
Eales disease
Flutter valve
Hypertrophic cardiomyopathy