[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Heart and vessels](https://durgical.com/en/embryology/#a-heart) › Atrial septal defect and patent foramen ovale [Embryology](https://durgical.com/en/embryology/) · [Heart and vessels](https://durgical.com/en/embryology/#a-heart) # Atrial septal defect and patent foramen ovale - Malformation A hole between the atria lets blood pass from left to right; it often causes no symptoms until adulthood. Updated 2026-11-01 **See it in 3D:** [Interatrial septum](https://durgical.com/en/anatomy/interatrial-septum/) · [Right atrium](https://durgical.com/en/anatomy/right-atrium/) · [Left atrium](https://durgical.com/en/anatomy/left-atrium/) · [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/) · [Pulmonary veins](https://durgical.com/en/anatomy/pulmonary-veins/) ## Key points - Ostium secundum: the most common; excess resorption of the septum primum or a short septum secundum. - Ostium primum: the septum primum fails to join the endocardial cushions; part of the AV canal spectrum (Down syndrome). - Sinus venosus: near the superior vena cava; usually with anomalous drainage of right pulmonary veins. - Acyanotic; fixed split second heart sound and a pulmonary flow murmur. - Patent foramen ovale (about 25 % of adults): risk of paradoxical embolism and stroke. - Holt-Oram syndrome (TBX5): ASD plus thumb and forearm anomalies. ## What it is An atrial septal defect (ASD) is missing tissue in the interatrial septum that allows a left-to-right shunt. It is acyanotic and usually silent in childhood, so many are diagnosed in adults. A patent foramen ovale is not a true ASD: the septum is complete but its two layers never fused. ## Embryological cause - Weeks 5–6: if cell death in the septum primum is excessive, the ostium secundum is too large and the septum secundum can't cover it. - If the septum secundum is underdeveloped, it also fails to cover the ostium secundum: secundum ASD. - If the septum primum fails to fuse with the endocardial cushions, the ostium primum persists: primum ASD. - If the sinus venosus is poorly absorbed into the right atrium, a high sinus venosus ASD remains. - Patent foramen ovale: both layers exist but do not seal after birth. ## Markers - TBX5 - NKX2-5 - GATA4 ## How it presents - Infants and children: almost always asymptomatic; found because of a murmur. - Adults: exercise intolerance, palpitations, atrial fibrillation. - Large unrepaired defects: pulmonary hypertension and, rarely, shunt reversal (Eisenmenger). - Patent foramen ovale: cryptogenic stroke in young people from paradoxical embolism. ## Diagnosis - Color Doppler echocardiography; transesophageal echo defines sinus venosus defects better. - Agitated saline (bubble) study for a patent foramen ovale. - ECG: incomplete right bundle branch block; left axis in primum defects. ## Memory aid In an ASD the second heart sound is stuck like a jammed door: the extra volume enters the right side every beat, breathing or not. ## Test yourself Think of the answer, then tap the question to see it. ## What is the embryological cause of a secundum ASD? Excessive resorption of the septum primum or underdevelopment of the septum secundum, leaving the ostium secundum open. ## Which malformation is a primum ASD related to? The atrioventricular canal defect: the septum primum fails to fuse with the endocardial cushions. ## Which auscultatory sign is typical of an ASD? A fixed split second heart sound that does not change with breathing. ## How does a patent foramen ovale differ from an ASD? No tissue is missing: the layers exist but never fused, and the passage opens only when right-sided pressure rises. [Add to my cards (4)](https://durgical.app/estudiar/?add=/en/embryology/atrial-septal-defect-and-patent-foramen-ovale/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Interatrial septum](https://durgical.com/en/anatomy/interatrial-septum/) - [Right atrium](https://durgical.com/en/anatomy/right-atrium/) - [Left atrium](https://durgical.com/en/anatomy/left-atrium/) - [Right ventricle](https://durgical.com/en/anatomy/right-ventricle/) - [Pulmonary veins](https://durgical.com/en/anatomy/pulmonary-veins/) ## Related - [Atrial septation: septum primum, septum secundum and foramen ovale](https://durgical.com/en/embryology/atrial-septation-septum-primum-septum-secundum-and-foramen-ovale/) - [Atrioventricular septal defect (endocardial cushion defect)](https://durgical.com/en/embryology/atrioventricular-septal-defect/) - [Ventricular septal defect](https://durgical.com/en/embryology/ventricular-septal-defect/) - [Fetal circulation and the changes at birth](https://durgical.com/en/embryology/fetal-circulation-and-the-changes-at-birth/) - [Ebstein anomaly](https://durgical.com/en/embryology/ebstein-anomaly/) ## Related conditions - [Atrial septal defect](https://durgical.com/en/conditions/atrial-septal-defect/) - [Ischaemic stroke](https://durgical.com/en/conditions/ischaemic-stroke/) - [Pulmonary hypertension and cor pulmonale](https://durgical.com/en/conditions/pulmonary-hypertension-and-cor-pulmonale/) - [Down syndrome (trisomy 21)](https://durgical.com/en/conditions/down-syndrome/) [← All of embryology](https://durgical.com/en/embryology/) Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given. Sources: Langman's Medical Embryology, 13th ed., ch. 13: Cardiovascular System (Wolters Kluwer, 2015); [Atrial Septal Defect (ASD) | Congenital Heart Defects (CHDs) | CDC](https://www.cdc.gov/heart-defects/about/atrial-septal-defect.html) (Centers for Disease Control and Prevention, 2024). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/embryology/atrial-septal-defect-and-patent-foramen-ovale/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/atrial-septal-defect-and-patent-foramen-ovale/