[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anatomy](https://durgical.com/en/anatomy/) › [Chest](https://durgical.com/en/anatomy/region/chest/) › Interatrial septum [Cardiovascular system](https://durgical.com/en/anatomy/system/cardiovascular-system/) · [Chest](https://durgical.com/en/anatomy/region/chest/) # Interatrial septum The interatrial septum is the thin wall between the two upper chambers of the heart; its oval dip marks an opening that closed after birth. [See in 3D →](https://durgical.app/?from=durgipedia&lang=en#region=thorax&select=interatrial_septum&side=r) Opens in the Durgical app, no sign-up needed. ## What it is The thin wall between the two atria, with a shallow dip (the fossa ovalis) where a fetal opening closed after birth. ## What it does Separates the atria. In about 1 in 4 adults the fetal flap is not fully sealed (patent foramen ovale). ## Key points - The fossa ovalis floor is the old septum primum; its raised rim (limbus) is the edge of the septum secundum - A patent [foramen ovale](https://durgical.com/en/anatomy/foramen-ovale/) is a flap that never sealed, not missing tissue; it opens when right atrial pressure rises (cough, straining), allowing paradoxical embolism - Secundum atrial septal defect, at the fossa ovalis, is the commonest type; it gives a wide, fixed split second heart sound ## Key facts **Where** Between atria; fossa ovalis with limbus on right atrial side **Function** Separates atria; fossa ovalis is remnant of fetal foramen ovale (right-to-left shunt); probe-patent in about 25% of adults ## Relations **In front** Aortic root at the [aortic non-coronary cusp](https://durgical.com/en/anatomy/non-coronary-leaflet-of-aortic-valve/), bulging against its front part **Above** Opening of the [superior vena cava](https://durgical.com/en/anatomy/superior-vena-cava/), where a sinus venosus defect lies **Below** [Inferior vena cava](https://durgical.com/en/anatomy/inferior-vena-cava/) and [coronary sinus](https://durgical.com/en/anatomy/coronary-sinus/) openings; below lies the atrioventricular septum with the triangle of Koch and the [Atrioventricular (AV) node](https://durgical.com/en/anatomy/atrioventricular-node/) **Behind** Interatrial groove on the back of the heart, behind which the right [pulmonary veins](https://durgical.com/en/anatomy/pulmonary-veins/) enter the [left atrium](https://durgical.com/en/anatomy/left-atrium/); surgeons open this groove to reach the left atrium and mitral valve ## How to find it From the opened [right atrium](https://durgical.com/en/anatomy/right-atrium/) it is the oval dip on the medial wall, above the inferior vena cava opening, with the limbus felt as a ridge. In the catheter laboratory the fossa ovalis is the thinnest point and the site of transseptal puncture into the left atrium. ## On imaging Echocardiography: subcostal views in children and transesophageal echo in adults show it best; colour Doppler and an agitated saline (bubble) study show a shunt. A large atrial septal defect dilates the right atrium and [right ventricle](https://durgical.com/en/anatomy/right-ventricle/) and enlarges the [pulmonary arteries](https://durgical.com/en/anatomy/right-pulmonary-artery/) on X-ray. ## Common problems - Patent foramen ovale, usually harmless; sometimes closed with a device after certain strokes. - Atrial septal defect (a true hole). ## How it is diagnosed Echocardiogram; ECG for rhythm problems. ## Treatment - Treatment of the underlying cause; catheter ablation for atrial flutter. ## Clinical notes - Transseptal puncture through the fossa ovalis gives catheter access to the left atrium for ablation, mitral procedures and appendage closure - Selected secundum defects and some patent foramen ovale after certain strokes are closed with a catheter device; primum and sinus venosus defects lack rims and are repaired surgically - A large unrepaired atrial septal defect leads to right heart dilation, atrial arrhythmias and, late, pulmonary hypertension with shunt reversal (Eisenmenger syndrome) ## Anatomical variants - Atrial septal aneurysm: a floppy fossa ovalis that bulges from side to side, often with a patent foramen ovale - The fossa ovalis varies in shape (oval, round or elliptical) and size ## Development The septum primum grows down and its upper part breaks open (ostium secundum); the septum secundum grows to its right, leaving the foramen ovale. At birth, higher left atrial pressure presses the two together. ## Related conditions - [Cardiac tumours (atrial myxoma)](https://durgical.com/en/conditions/cardiac-tumours/) - [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/) - [Atrial septal defect](https://durgical.com/en/conditions/atrial-septal-defect/) ## Test yourself Think of the answer, then tap the question to see it. ## What forms the floor and the rim (limbus) of the fossa ovalis? The floor is the old septum primum; the limbus is the edge of the septum secundum. ## What is a patent foramen ovale, and how can it cause paradoxical embolism? A flap that never sealed (probe-patent in about 25% of adults); it opens when right atrial pressure rises, as with cough or straining. ## Which atrial septal defect is commonest, and what heart sound does it give? The secundum defect, at the fossa ovalis; it gives a wide, fixed split second heart sound. ## Where is transseptal puncture made to reach the left atrium? Through the fossa ovalis of the interatrial septum, its thinnest point. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anatomy/interatrial-septum/) Educational information, not medical advice. For any symptom, see a health professional. ## Its names **Official Latin (TA2)** septum interatriale; fossa ovalis atrii dextri TA2 3964 **Official Spanish (DeCS)** Tabique interatrial DeCS D054087 **English (TA2)** Interatrial septum **Also called** oval fossa of right atrium · atrial septum · septum atriorum ## Related - [Atrioventricular (AV) node](https://durgical.com/en/anatomy/atrioventricular-node/) Sources: Terminologia Anatomica (TA2); [DeCS](https://decs.bvsalud.org/es/ths/resource/?id=52515); [Anatomy, Thorax, Heart Fossa Ovalis](https://www.ncbi.nlm.nih.gov/books/NBK538432/); [Anatomy, Thorax, Heart Foramen Ovale](https://www.ncbi.nlm.nih.gov/books/NBK545203/); Tratado de anatomía humana (9.ª ed.), tomo II, Libro IV Angiología, sección 1, capítulo 1: Corazón, artículos I–VI. ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. 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