Atrial Septum: Definition, Uses, and Clinical Overview

Posted on February 27, 2026 | by drspine

Atrial Septum Introduction (What it is)

The Atrial Septum is the wall that separates the heart’s two upper chambers (the right atrium and left atrium).
It helps keep oxygen-poor blood and oxygen-rich blood moving through the correct sides of the heart.
Clinicians refer to it when interpreting heart imaging and when planning certain catheter-based procedures.
It is also a key focus in some congenital heart conditions (present from birth).

Why Atrial Septum used (Purpose / benefits)

The Atrial Septum is “used” in clinical medicine mainly as an anatomic landmark and as a structure whose integrity matters for normal circulation. Its purpose in the body is to separate the right-sided and left-sided atria so blood flows efficiently through the lungs and then out to the body.

In practice, clinicians focus on the Atrial Septum because:

It can have natural openings or defects that allow blood (or bubbles/clots) to pass between atria, which may affect symptoms and long-term heart function.
It provides a pathway for advanced procedures: many left atrial catheter procedures (for example, some rhythm treatments and structural heart interventions) access the left atrium by crossing the Atrial Septum.
It helps explain certain symptoms and findings, such as shortness of breath, exercise intolerance, a heart murmur, or right-sided heart enlargement on imaging.
It supports risk assessment in selected scenarios, such as evaluating possible right-to-left flow (shunting) or assessing anatomy relevant to stroke workups.

Overall, attention to the Atrial Septum helps clinicians with diagnosis, physiologic interpretation (how blood is moving), procedural planning, and—when needed—structural repair.

Clinical context (When cardiologists or cardiovascular clinicians use it)

Common scenarios where the Atrial Septum is referenced, assessed, or intentionally crossed include:

Evaluation of a heart murmur, especially when imaging suggests abnormal atrial-level blood flow
Workup of right atrial/right ventricular enlargement or unexplained increased blood flow to the lungs
Assessment of atrial septal defect (ASD) or patent foramen ovale (PFO) as congenital or incidental findings
Evaluation in selected patients with unexplained stroke where an atrial-level connection is being considered
Investigation of low oxygen levels in specific circumstances where right-to-left shunting is suspected
Planning catheter ablation for certain atrial arrhythmias (often requiring access to the left atrium)
Planning structural heart procedures that use transseptal access (crossing the Atrial Septum to reach the left atrium)
Follow-up after prior congenital heart repair, including surgical patches or prior closure devices
Pre-procedural mapping of anatomy using echocardiography, cardiac CT, or cardiac MRI

Contraindications / when it’s NOT ideal

The Atrial Septum itself is a normal structure, so “contraindications” usually apply to interventions involving the Atrial Septum (such as device closure of a defect or intentionally crossing it with catheters). Whether an approach is suitable varies by clinician and case.

Situations where an atrial septum–related intervention may be less suitable, deferred, or approached differently include:

Anatomy not favorable for catheter closure of an ASD (for example, certain defect types or inadequate surrounding tissue rims to anchor a device)
Very large or complex defects or associated congenital abnormalities where surgical repair may be considered instead
Severe pulmonary hypertension with physiology where closing an interatrial connection could be poorly tolerated (assessment is individualized)
Intracardiac thrombus (blood clot) concern, especially in the left atrium, where crossing the septum may increase embolic risk
Active infection involving the bloodstream or heart structures (timing and approach vary)
Prior atrial septal patch or closure device that complicates repeat transseptal access (alternative strategies may be used)
Unfavorable venous access or vascular anatomy affecting catheter-based approaches
Need for other heart surgery for separate reasons, where combining repairs surgically may be considered

How it works (Mechanism / physiology)

The Atrial Septum is a partition between the atria, but it is not just “a wall”—it is part of a pressure-and-flow system.

Core physiologic principle: pressure differences and shunting

Under typical conditions, left atrial pressure is slightly higher than right atrial pressure.
If there is an opening (such as an ASD), blood often flows from left to right (left-to-right shunt), increasing blood volume returning to the right heart and lungs. Over time, this can contribute to right-sided chamber enlargement in some patients.
In certain situations, right-sided pressures can rise and the direction can become right-to-left, allowing less-oxygenated blood to enter the left atrium and systemic circulation, potentially lowering oxygen levels.

Relevant anatomy around the Atrial Septum

The Atrial Septum lies between the right atrium and left atrium.
A key region is the fossa ovalis, a thinner area that is the remnant of fetal circulation.
Nearby structures clinicians think about include:
The superior and inferior vena cava (blood returning to the right atrium)
The pulmonary veins (oxygen-rich blood entering the left atrium)
The tricuspid and mitral valves (between atria and ventricles)
The conduction system (electrical pathways), which is relevant because procedures near the atria can influence rhythm

Fetal remnant and “flap” physiology (PFO concept)

Before birth, the atria communicate through a fetal opening that helps bypass the lungs. After birth, this typically seals. If a small flap-like connection persists, it may be called a patent foramen ovale (PFO). A PFO is not the same as a true tissue defect like many ASDs; it is more like a potential tunnel that can open under certain pressure conditions.

Clinical interpretation over time

The Atrial Septum does not “wear out” in a typical sense, but defects, stretching, or remodeling can change hemodynamics over time.
After transseptal procedures, a small iatrogenic atrial septal defect (created by catheter crossing) may be seen; it often closes over time, though persistence can occur depending on factors such as puncture size, technique, and patient anatomy.

Atrial Septum Procedure overview (How it’s applied)

The Atrial Septum is not itself a procedure, but it is commonly assessed and sometimes crossed or repaired. A typical clinical workflow looks like this (details vary by clinician and case):

Evaluation / exam – Symptom review (for example, shortness of breath, exercise limitation, palpitations) and physical exam – Baseline tests such as ECG – Initial imaging often begins with transthoracic echocardiography (TTE)
Targeted assessment – If more detail is needed, clinicians may use:
- Transesophageal echocardiography (TEE) for closer views
- Bubble study (agitated saline) to detect interatrial passage under certain conditions
- Cardiac CT or MRI in selected cases to define anatomy and chamber size
Preparation (if an intervention is planned) – Pre-procedure planning focuses on anatomy, vascular access, rhythm, and blood-thinner considerations (management varies by clinician and case) – Imaging guidance strategy is selected (for example, TEE or intracardiac echocardiography)
Intervention / testing (examples) – Catheter-based closure of an ASD/PFO (when appropriate): catheters are guided through the veins to the right atrium and across/into the defect region, and a closure device may be deployed under imaging guidance. – Transseptal access (crossing the Atrial Septum intentionally): a controlled puncture allows catheters to reach the left atrium for procedures such as certain ablations or structural interventions.
Immediate checks – Imaging is used to confirm device position (if placed), assess for residual shunt, and evaluate for pericardial fluid or other acute concerns – Rhythm and vital signs are monitored
Follow-up – Repeat imaging may be scheduled to assess healing, closure status, and chamber remodeling over time – Ongoing follow-up depends on the underlying condition and the intervention performed

Types / variations

“Atrial septum” can refer to normal anatomy, congenital variants, or post-procedural changes. Clinically common variations include:

Normal anatomic regions

Fossa ovalis (thin central portion)
Thicker muscular rims surrounding the fossa ovalis region

Congenital interatrial communications

Patent foramen ovale (PFO): a flap-like potential channel rather than a missing tissue hole
Atrial septal defect (ASD): a true defect in septal tissue, with subtypes such as:
Secundum ASD (often in the region of the fossa ovalis)
Primum ASD (often associated with atrioventricular septal anatomy and valve considerations)
Sinus venosus ASD (near venous inflow regions and sometimes associated with anomalous pulmonary venous return)
Coronary sinus–type defects (uncommon, involving the coronary sinus region)

Morphologic features that may be reported on imaging

Atrial septal aneurysm: increased mobility/bowing of septal tissue (definition varies by imaging criteria)
Multiple fenestrations: more than one small opening
Rim adequacy: the amount of surrounding tissue to support closure devices (important for planning)

Acquired or iatrogenic changes

Post-transseptal iatrogenic ASD (created during catheter access)
Surgical patches or closure devices from prior repairs, which can alter future access routes and imaging appearance

Pros and cons

Pros:

Helps maintain efficient circulation by separating right- and left-sided atrial blood under normal anatomy
Provides a clear imaging landmark for diagnosing shunts and interpreting chamber enlargement patterns
Can be a target for structural repair (surgical or catheter-based) when a defect is clinically significant
Enables transseptal access to the left atrium for certain rhythm and structural heart procedures
When defects are treated appropriately, it may reduce volume overload on the right heart in selected patients
Assessment can often be done with noninvasive imaging as a first step (for example, TTE)

Cons:

Defects or abnormal communications can lead to abnormal blood flow (shunting) and long-term chamber remodeling in some cases
Not all atrial septal anatomy is suitable for catheter-based closure; some cases require surgery or monitoring
Interventions involving the septum (closure or transseptal puncture) carry procedural risks such as bleeding, rhythm disturbances, vascular complications, or injury to nearby structures (risk varies by clinician and case)
Some patients may have residual shunting after intervention, requiring follow-up imaging
Atrial-level interventions can be associated with new or recurrent atrial arrhythmias in some patients (risk depends on baseline rhythm and atrial size)
Prior patches/devices can make later procedures more complex and imaging interpretation more nuanced

Aftercare & longevity

Aftercare depends on whether the issue is simply an anatomic finding (observed), a congenital defect being monitored, or an intervention that crossed or repaired the Atrial Septum.

Factors that commonly influence longer-term outcomes include:

Underlying diagnosis and severity (PFO vs ASD subtype, defect size, degree of shunt)
Right heart size and function and whether there is established remodeling
Pulmonary pressures and coexisting lung or vascular disease
Heart rhythm history, especially atrial fibrillation or other atrial tachyarrhythmias
Follow-up imaging adherence, since echocardiography is often used to confirm stability or closure status
If a device is placed, outcomes may relate to device selection and anatomy (varies by material and manufacturer) and how well surrounding tissue supports healing
Comorbidities (for example, sleep apnea, hypertension, diabetes) that can influence cardiac structure and rhythm over time

Recovery timelines and activity limits after procedures vary by clinician and case, and they are typically guided by procedural access site healing, rhythm monitoring needs, and follow-up imaging plans.

Alternatives / comparisons

Because the Atrial Septum is an anatomic structure, “alternatives” usually refer to alternative evaluation methods or alternative ways of managing atrial-level findings.

Common comparisons include:

Observation/monitoring vs closure/repair
Some atrial septal findings are incidental and monitored with periodic imaging.
In other situations, closure (catheter-based or surgical) may be considered when there is meaningful shunting, symptoms, or physiologic impact. The threshold varies by clinician and case.
Catheter-based closure vs surgical repair
Catheter-based approaches avoid open surgery and are often used when anatomy is suitable.
Surgical repair may be preferred for complex anatomy, very large defects, or when additional cardiac repairs are needed.
Transthoracic echocardiography (TTE) vs transesophageal echocardiography (TEE)
TTE is noninvasive and commonly used first.
TEE can provide higher-detail views of the Atrial Septum and is often used for procedural planning or when TTE images are limited.
Bubble study vs color Doppler
Color Doppler can show direction and pattern of flow across a defect.
Bubble study can help detect intermittent or positional right-to-left passage, especially relevant in PFO assessment.
Transseptal access vs alternative catheter routes
Many left atrial procedures use transseptal access.
Some interventions may use different routes (depending on the target structure), but feasibility depends on anatomy and the specific procedure.

Atrial Septum Common questions (FAQ)

Q: Is the Atrial Septum a “valve” or a “membrane”?
No. The Atrial Septum is a wall made of heart tissue that separates the two atria. Some parts are thinner (like the fossa ovalis), which is why it can be described as membrane-like in places, but it is not a valve.

Q: Can you feel an atrial septal problem (like an ASD or PFO)?
Many people do not feel anything and the finding is discovered on imaging. When symptoms occur, they may be nonspecific—such as reduced exercise tolerance, shortness of breath, or palpitations—depending on the type of communication and the amount of shunting.

Q: How do clinicians check the Atrial Septum?
Echocardiography is the most common starting point. Depending on what needs to be clarified, clinicians may add a bubble study, TEE, or cross-sectional imaging such as cardiac CT or MRI.

Q: Does assessing the Atrial Septum hurt?
A standard transthoracic echocardiogram is typically painless. More invasive tests (like TEE) or catheter procedures involve sedation or anesthesia plans determined by the care team, and discomfort varies by test and person.

Q: If a closure device is used, how long does it last?
Closure devices are designed to be long-term implants. The durability and long-term results depend on patient anatomy, healing response, and device design; follow-up imaging is commonly used to confirm stability.

Q: Is it “safe” to cross the Atrial Septum during a procedure?
Transseptal access is a well-established technique in experienced centers, but it is still an invasive step with potential complications. The balance of benefits and risks varies by clinician and case, including anatomy and the specific procedure being performed.

Q: Will I need to stay in the hospital for an Atrial Septum–related procedure?
Hospital stay depends on the procedure type (diagnostic test vs catheter intervention vs surgery), the access site, and monitoring needs. Some catheter-based interventions may involve short observation, while surgical repair typically requires a longer stay.

Q: Are there activity restrictions afterward?
Restrictions depend on the access site (often a leg vein for catheter procedures), rhythm status, and whether a device was implanted. Timing and specifics vary by clinician and case and are usually based on healing and follow-up testing.

Q: What does “shunt” mean in plain language?
A shunt is an abnormal pathway that lets blood move between areas it normally would not. With the Atrial Septum, a shunt means blood can pass between the right and left atria through a defect or flap-like opening.

Q: What determines the cost of evaluation or treatment?
Cost varies widely by region, insurance coverage, facility, imaging modality, and whether treatment is medical, catheter-based, or surgical. Additional factors include anesthesia needs, hospital stay length, and follow-up testing.