lena hannaAUTHOR · HEART MOM
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THE LITTLE HEART GUIDE · SEPTEMBER 15, 2026

Different hearts.
A little more understanding.

ASD. VSD. TOF. A handful of letters can feel like a whole new language. Here is a friendly place to start.

What does “congenital” mean?

It means present at birth. A congenital heart defect, or CHD, is a difference in the heart’s structure that can affect blood flow. CHDs range from mild to complex. Nearly 1% of babies born in the United States have a CHD. Source: CDC overview.

SAVE A LITTLE SPACE FOR UNDERSTANDING

Six heart differences,
in plain language.

A selection of common and complex CHDs—not every diagnosis, and not a ranking of severity.

First, the usual route

  1. Body
  2. Right heart
  3. Lungs
  4. Left heart
  5. Body

The lungs add oxygen before blood returns to the left side of the heart and travels to the body. The diagrams below zoom in on each difference. Source: NIH.

ASD01

An opening

Atrial septal defect

ASD: where the difference is. An opening in the wall between the two upper chambers of the heart.
Simplified illustration; not to scale. Select the drawing to view it full size. The person’s right is on your left.

An opening in the wall between the two upper chambers of the heart.

Compare with typical anatomyASD: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.FOUR CHAMBERS · FRONT VIEWRight atriumLeft atriumRight ventricleLeft ventricleupper chamberupper chamberlower chamberlower chamberThe wall separates the two sides.
CDC: atrial septal defect ↗
VSD02

An opening

Ventricular septal defect

VSD: where the difference is. An opening in the wall between the two lower chambers of the heart.
Simplified illustration; not to scale. Select the drawing to view it full size. The person’s right is on your left.

An opening in the wall between the two lower chambers of the heart.

Compare with typical anatomyVSD: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.FOUR CHAMBERS · FRONT VIEWRight atriumLeft atriumRight ventricleLeft ventricleupper chamberupper chamberlower chamberlower chamberThe wall separates the two sides.
CDC: ventricular septal defect ↗
PDA03

A connection stays open

Patent ductus arteriosus

PDA: where the difference is. A blood vessel connecting the aorta and pulmonary artery before birth stays open after birth.
Simplified illustration; not to scale. Select the drawing to view it full size.

A blood vessel connecting the aorta and pulmonary artery before birth stays open after birth.

Compare with typical anatomyPDA: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.To lungs ↑To body ↑Pulmonary arteryAortaAfter normal closure: no open connection.
NIH: types of heart defects ↗
PS04

A narrowed passage

Pulmonary stenosis

PS: where the difference is. A narrowed or stiff pulmonary valve restricts blood flow from the heart toward the lungs.
Simplified illustration; not to scale. Select the drawing to view it full size.

A narrowed or stiff pulmonary valve restricts blood flow from the heart toward the lungs.

Compare with typical anatomyPS: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.PULMONARY VALVE · CLOSE-UPA wider passage for bloodRight ventricle → valve → toward lungs
NIH: types of heart defects ↗
CoA05

A narrowed passage

Coarctation of the aorta

CoA: where the difference is. Part of the aorta—the artery carrying oxygen-rich blood to the body—is narrower than usual. The heart must work harder to push blood through.
Simplified illustration; not to scale. Select the drawing to view it full size.

Part of the aorta—the artery carrying oxygen-rich blood to the body—is narrower than usual. The heart must work harder to push blood through.

Compare with typical anatomyCoA: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.AORTA · CLOSE-UPA wider passage for bloodFrom the heart → aorta → toward the body
CDC: coarctation of the aorta ↗
TOF06

Four differences together

Tetralogy of Fallot

TOF: where the difference is. A VSD; narrowing toward the lungs; an aorta positioned over the VSD, receiving blood from both lower chambers; and a thickened right lower chamber muscle. Together, these can reduce the oxygen reaching the body.
Simplified illustration; not to scale. Select the drawing to view it full size. The person’s right is on your left.

A VSD; narrowing toward the lungs; an aorta positioned over the VSD, receiving blood from both lower chambers; and a thickened right lower chamber muscle. Together, these can reduce the oxygen reaching the body.

  1. Opening: a VSD between the lower chambers.
  2. Narrow exit: the route toward the lungs is restricted.
  3. Shifted aorta: it sits over the VSD and can receive blood from both lower chambers.
  4. Thicker muscle: the right ventricle’s wall becomes thicker.
Compare with typical anatomyTOF: typical anatomy for comparisonThe same simplified view without the highlighted defect: intact walls, separate arteries, and open passages.To lungs ↑To body ↑RightventricleLeftventricleLower chambers and outflow only; upper chambers omitted.
CDC: tetralogy of Fallot ↗

The same diagnosis can look different from person to person. Your child’s heart team can explain their individual anatomy and care.

A repair is part of a longer story.

Better treatment means more people with CHDs are living longer. But a repair does not always mean a cure; ongoing heart care can still matter. Some defects have few noticeable symptoms, and some are found before birth or through newborn screening. Source: CDC overview.

Three questions to bring along

  • Can you draw my child’s heart and show me how the blood flows?
  • What follow-up does this particular diagnosis need?
  • Which changes should prompt a call to our care team?

You do not have to learn every abbreviation today. Start with the one in front of you, ask the next question, and keep this guide nearby.

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