Skip to content
How It Works
Explore
Resources Ask a Question
Who It's For
Patients
Decode results, prep for appointments, weigh options.
Caregivers & advocates
Carry the research load for someone you love.
Providers & clinicians
Resources for patients in your practice.
Log In Ask a Question
PubMed This is a summary of 19 peer-reviewed journal articles Updated
Cardiology

The Heart's Blueprint: Types and Biology of "Holes"

At a Glance

A Patent Foramen Ovale (PFO) is a flap that fails to seal after birth, while an Atrial Septal Defect (ASD) is a structural hole in the heart wall. Secundum ASDs can often be closed with a catheter device, whereas Primum, Sinus Venosus, and Coronary Sinus ASDs typically require surgery.

To understand why some heart “holes” are treated with a simple catheter and others require surgery, it helps to look at the heart’s blueprints. While they all allow blood to pass between the upper chambers, their biological origin and anatomical location determine the entire treatment plan [1][2].

The Biological Difference: Flap vs. Deficiency

The heart wall that separates the upper chambers (the atrial septum) is not a single piece of tissue; it forms from two separate “curtains” that overlap during development [3].

  • PFO (The Failed Seal): A Patent Foramen Ovale is a biological “leftover.” In the womb, everyone has this flap-like opening to let blood bypass the lungs [3]. After birth, when the baby takes their first breath, the pressure on the left side of the heart usually pins these two curtains together, and they eventually fuse shut [3]. A PFO occurs when they touch but fail to “zip” together [4].
  • ASD (The Structural Deficiency): Unlike a PFO, an Atrial Septal Defect is a true structural deficiency [1]. Part of the heart wall is actually missing or didn’t grow enough to reach the other side, leaving a permanent gap [1][4].

The Four Main Types of ASD

Doctors categorize ASDs by where they are located on that wall. Their location is the most important factor in deciding the type of repair needed [5].

1. Secundum ASD (Most Common)

Located right in the middle of the wall (the fossa ovalis) [1]. Because it is surrounded by a “rim” of heart tissue, it is the only type that can usually be fixed with a transcatheter device—a tiny plug delivered through a vein in the leg [5][6].

2. Primum ASD

Located at the very bottom of the wall, near the heart’s valves [1]. These are often associated with issues in the mitral valve (the door between the left-side chambers) [7]. Because there is no “bottom rim” to hold a plug, and because the valves often need repair, this type requires surgical closure [8][9].

3. Sinus Venosus ASD

Located at the very top or bottom of the wall, where the large veins (the vena cava) enter the heart [1]. This type is frequently linked to PAPVR (Partial Anomalous Pulmonary Venous Return), a condition where the veins from the lungs are connected to the wrong side of the heart [10][11]. Surgery is required to redirect these veins and close the gap [12][10].

4. Coronary Sinus ASD (Rare)

Located where the heart’s own “sewer system” (the coronary sinus) drains into the atrium [1]. In this case, the wall between the drainage vein and the left atrium is missing, which requires a specialized surgical repair [1].

Grading the Severity

When a doctor reviews the imaging (like an echocardiogram or cardiac MRI), they look at three main metrics to “grade” the defect:

  • Size: Usually measured in millimeters. While there is no universal cutoff, “large” defects are more likely to cause symptoms early in life [13][14].
  • Shunt Fraction (Qp:Qs): This is a mathematical ratio that compares the amount of blood going to the lungs (Qp) versus the body (Qs) [15]. A ratio of 1.5:1 or higher means 50% more blood is going to the lungs than should be, which is a common threshold for recommending closure [16][17].
  • Right Heart Effect: The doctor looks for dilation—stretching or enlargement of the right ventricle—which is a physical sign that the heart is struggling with the extra volume [18][19].

Return to the Home Page

Common questions in this guide

What is the difference between a PFO and an ASD?
A Patent Foramen Ovale (PFO) is a natural flap-like opening that fails to close completely after birth. An Atrial Septal Defect (ASD) is a structural deficiency where a portion of the heart wall is missing or underdeveloped.
Can all atrial septal defects be fixed without surgery?
No. Only secundum ASDs, which are located in the middle of the heart wall and have a rim of tissue, can typically be closed with a transcatheter device. Other types, such as primum and sinus venosus ASDs, require open heart surgery.
What does the Qp:Qs ratio mean on my echocardiogram?
The Qp:Qs ratio measures the amount of blood going to the lungs compared to the rest of the body. A ratio of 1.5:1 or higher indicates that 50 percent more blood is flowing to the lungs than normal, which is often a threshold for doctors to recommend closing the defect.
What is a secundum ASD?
A secundum ASD is the most common type of atrial septal defect, located right in the middle of the wall between the heart's upper chambers. Because it is surrounded by a rim of tissue, it can often be treated with a tiny plug delivered through a catheter.
Why does an ASD cause right heart enlargement?
An ASD allows extra blood to flow from the left side of the heart into the right side. Over time, this extra volume of blood can stretch and dilate the right ventricle because the heart is forced to work harder to pump the excess fluid.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.Which of the four types of ASD does my child (or do I) have?
  2. 2.Are there any signs of PAPVR, or are all the pulmonary veins connected correctly?
  3. 3.Is the defect's location suitable for a catheter-based (percutaneous) closure, or will surgery be required?
  4. 4.What is the 'Qp:Qs' ratio, and how does it reflect the amount of extra blood going to the lungs?
  5. 5.Are the 'rims' or edges of the defect strong and large enough to hold a closure device in place?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (19)
  1. 1

    Anatomy of the atrial septum and interatrial communications.

    Naqvi N, McCarthy KP, Ho SY

    Journal of thoracic disease 2018; (10(Suppl 24)):S2837-S2847 doi:10.21037/jtd.2018.02.18.

    PMID: 30305943
  2. 2

    Patent Foramen Ovale and Atrial Septal Defect.

    Aoun J, Hatab T, Volpi J, Lin CH

    Cardiology clinics 2024; (42(3)):417-431 doi:10.1016/j.ccl.2024.02.019.

    PMID: 38910025
  3. 3

    Patent Foramen Ovale-A Not So Innocuous Septal Atrial Defect in Adults.

    Romano V, Gallinoro CM, Mottola R, et al.

    Journal of cardiovascular development and disease 2021; (8(6)) doi:10.3390/jcdd8060060.

    PMID: 34070460
  4. 4

    The Congenital Malformation of the Interatrial Septum-A Review of Its Development and Embryology with Clinical Implications.

    Oliveira RC, Martins P, Martins MF

    Journal of developmental biology 2025; (13(3)) doi:10.3390/jdb13030028.

    PMID: 40843896
  5. 5

    Transcatheter and intraoperative device closure and surgical repair for atrial septal defect.

    Qiu HF, Chen Q, Hong ZN, et al.

    Journal of cardiothoracic surgery 2019; (14(1)):136 doi:10.1186/s13019-019-0957-0.

    PMID: 31324190
  6. 6

    Atrial septal defect closure: indications and contra-indications.

    Fraisse A, Latchman M, Sharma SR, et al.

    Journal of thoracic disease 2018; (10(Suppl 24)):S2874-S2881 doi:10.21037/jtd.2018.08.111.

    PMID: 30305947
  7. 7

    Identification and Morphogenesis of Vestibular Atrial Septal Defects.

    Loomba RS, Tretter JT, Mohun TJ, et al.

    Journal of cardiovascular development and disease 2020; (7(3)) doi:10.3390/jcdd7030035.

    PMID: 32927616
  8. 8

    Surgical closure of atrial septal defects.

    Liava'a M, Kalfa D

    Journal of thoracic disease 2018; (10(Suppl 24)):S2931-S2939 doi:10.21037/jtd.2018.07.116.

    PMID: 30305953
  9. 9

    Robot-Assisted Partial Atrioventricular Canal Defect Repair and Cryo-Maze Procedure.

    Mandal K, Srivastava AR, Nifong LW, Chitwood WR

    The Annals of thoracic surgery 2016; (101(2)):756-8.

    PMID: 26777933
  10. 10

    Neglected Partial Anomalous Pulmonary Venous Return during Atrial Septal Defect Device Closure.

    Radmehr E, Radmehr H, Shahidi M, Sayadpour Zanjani K

    The journal of Tehran Heart Center 2023; (18(3)):228-231 doi:10.18502/jthc.v18i3.14119.

    PMID: 38146408
  11. 11

    Clinical Significance of Partial Anomalous Pulmonary Venous Connections (Isolated and Atrial Septal Defect Associated) Determined by Cardiovascular Magnetic Resonance.

    Hatipoglu S, Almogheer B, Mahon C, et al.

    Circulation. Cardiovascular imaging 2021; (14(8)):e012371 doi:10.1161/CIRCIMAGING.120.012371.

    PMID: 34384233
  12. 12

    Transcatheter closure of sinus venosus atrial septal defect with anomalous pulmonary venous drainage: Innovative technique with long-term follow-up.

    Abdullah HAM, Alsalkhi HA, Khalid KA

    Catheterization and cardiovascular interventions : official journal of the Society for Cardiac Angiography & Interventions 2020; (95(4)):743-747 doi:10.1002/ccd.28364.

    PMID: 31197932
  13. 13

    Interatrial Communications: Prevalence and Subtypes in 12,385 Newborns-a Copenhagen Baby Heart Study.

    Blixenkrone-Møller E, Dannesbo S, Dehn AM, et al.

    Pediatric cardiology 2025; (46(6)):1570-1580 doi:10.1007/s00246-024-03571-0.

    PMID: 39003423
  14. 14

    Transcatheter closure for decompression sickness with a patent foramen ovale: A case report.

    Jiang F

    Journal of interventional medicine 2021; (4(3)):149-151 doi:10.1016/j.jimed.2021.05.004.

    PMID: 34805964
  15. 15

    Secundum atrial septal defects in adults: all you need to know with an emphasis on outcome.

    Shaban Q, Hijazi ZM

    Expert review of cardiovascular therapy 2025; (23(4)):165-178 doi:10.1080/14779072.2025.2495235.

    PMID: 40285490
  16. 16

    Echocardiographic Z-Score to Predict Pulmonary-Systemic Flow Ratio in Children With Atrial Septal Defect.

    Sumitomo NF, Kodo K, Maeda J, et al.

    Circulation reports 2025; (7(10)):956-964 doi:10.1253/circrep.CR-25-0119.

    PMID: 41081265
  17. 17

    The correlation between serum level of brain natriuretic peptide and amount of left to right shunt.

    Jamei Khosroshahi A, Molaei A, Samadi M, Eskandartash E

    Journal of cardiovascular and thoracic research 2019; (11(1)):68-71 doi:10.15171/jcvtr.2019.11.

    PMID: 31024675
  18. 18

    A rare case of Lutembacher's syndrome presenting with low-gradient severe mitral stenosis: case report and literature overview.

    El-Mhadi S, El Hajjaj B, Laktib N, et al.

    European heart journal. Case reports 2024; (8(7)):ytae327 doi:10.1093/ehjcr/ytae327.

    PMID: 39035253
  19. 19

    Pulmonary Artery Remodelling Assessed by Four-Dimensional Flow Magnetic Resonance Imaging in Pulmonary Arterial Hypertension and Atrial Septal Defect.

    Valdeolmillos E, Fournier E, Sakhi H, et al.

    CJC pediatric and congenital heart disease 2025; (4(4)):189-197 doi:10.1016/j.cjcpc.2025.03.004.

    PMID: 41608409

This page explains the biology and types of ASD and PFO for educational purposes. Always consult your cardiologist or pediatric heart specialist to interpret your specific echocardiogram or MRI results.

Get notified when new evidence is published on Interatrial communication.

We monitor PubMed for new peer-reviewed studies on this topic and email a short summary when something meaningful changes.