Three openings, one shared logic
Three of the commonest lesions are openings between the two sides of the circulation. An atrial septal defect (ASD) is a hole in the wall between the two upper chambers. A ventricular septal defect (VSD) is a hole in the wall between the two lower chambers — the single most common congenital lesion of all. A patent ductus arteriosus (PDA) is the fetal connecting vessel between the aorta and the lung artery that failed to close after birth. All three are usually acyanotic, because they all do the same thing: let red blood leak from the high-pressure left side to the low-pressure right side.
That leak is the left-to-right shunt, and it is the central idea of this guide. Because the body still receives fully oxygenated red blood, the child stays pink and may have no symptoms for years. But the shunted blood is not wasted harmlessly — it makes an extra loop through the lungs. The lungs and the right heart end up handling far more blood than they were designed for, and that is where the long-term trouble comes from.
How they are found
Many of these openings announce themselves as a heart murmur — the sound of blood rushing through a place it should not be. A VSD classically makes a loud murmur heard low on the left chest; a small VSD can be the loudest of all, because a narrow jet is turbulent and noisy. An ASD is quieter and sneakier: the hole itself is silent, and the clue is the extra blood crossing the pulmonary valve plus a characteristically “split” second heart sound. A PDA produces a continuous “machinery” murmur that runs through both phases of the heartbeat.
- A clinician hears a murmur, or a parent notices fast breathing and poor feeding in an infant.
- An echocardiogram is performed — an ultrasound of the heart that shows the hole and uses colour Doppler to display the shunt direction.
- Doctors estimate how big the shunt is — small leaks are watched, larger ones are planned for closure.
What happens over time — and how they close
Size and location drive the outcome. Many small VSDs close by themselves in early childhood, and a small ASD may cause no trouble for decades. A large hole, though, sends so much extra blood through the lungs that the right heart enlarges, the lungs become congested, and an infant may breathe fast, sweat with feeds, and grow slowly. The most important reason to fix a big long-standing shunt is to protect the lungs: years of overflow can permanently stiffen the lung arteries, a serious complication covered in the final guide.
Closing these defects has become remarkably gentle. Many ASDs and PDAs are now sealed without open surgery: a cardiologist threads a thin catheter up a vein, parks a small umbrella-like device or coil in the hole, and the tissue grows over it. A PDA in a premature newborn can sometimes be coaxed shut with medication that mimics the natural closing signal. Larger or awkwardly placed VSDs still call for surgical patch repair on cardiopulmonary bypass — a well-established operation with excellent results.