Dr. Alessandro Giardini
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If you have been told that your baby has a serious heart condition, or you are waiting for answers after a scan, it is completely natural to feel overwhelmed. Words like "transposition," "single ventricle" or "hypoplastic left heart" can sound frightening, and the uncertainty of not knowing what lies ahead can be one of the hardest parts for families. The most important thing to understand is this: many complex heart conditions in newborns are now well recognised, carefully managed and treated with outcomes that have improved dramatically over the past two decades. With the right specialist care, most babies go on to grow, develop and live active lives.
Dr Giardini is a Consultant Paediatric Cardiologist at Great Ormond Street Hospital, one of the world's leading paediatric cardiac centres. He regularly assesses newborns and infants with complex heart conditions and supports families from the moment of diagnosis through treatment and long-term follow-up, helping you understand clearly what is happening and what comes next.
Congenital heart defects are structural abnormalities of the heart that are present from birth. They are the most common type of birth defect, affecting approximately 1 in every 100 babies. Most congenital heart defects are mild, such as small holes in the heart that may close on their own. However, a smaller group are classified as complex or critical because they significantly affect how blood flows through the heart and lungs and may require treatment early in life.
In a normally formed heart, oxygen-poor blood returns to the right side, is pumped to the lungs to collect oxygen, returns to the left side, and is then pumped out to the body. Complex heart defects disrupt this circulation in different ways. Some conditions mean the great arteries are connected to the wrong chambers, sending blood along the wrong pathway. Others mean that one side of the heart has not developed properly and cannot do its share of the pumping work. Some involve the blood vessels draining back to the wrong part of the heart, and others involve a combination of several structural abnormalities.
There are many individual diagnoses within this group, but the conditions parents are most likely to hear about include the following.
Transposition of the great arteries (TGA) is one of the most common complex heart defects presenting in newborns. The two great arteries leaving the heart (the aorta and the pulmonary artery) are switched, so that the aorta arises from the right ventricle and the pulmonary artery from the left. This means oxygen-poor blood is pumped back to the body and oxygen-rich blood is sent back to the lungs in two parallel circuits that do not mix. Babies with TGA typically appear blue (cyanotic) soon after birth because insufficient oxygen is reaching the body. The condition requires urgent intervention, usually a balloon atrial septostomy (to create a hole between the upper chambers and allow mixing of blood) followed by an arterial switch operation within the first two weeks of life. The arterial switch is one of the great success stories of modern paediatric cardiac surgery, with survival rates exceeding 97% in experienced centres.
Hypoplastic left heart syndrome (HLHS) is a condition in which the left side of the heart, including the left ventricle, mitral valve and aortic valve, is severely underdeveloped and unable to support the body's circulation. HLHS is one of the most challenging diagnoses in paediatric cardiology, but outcomes have improved substantially. Treatment involves a staged surgical pathway, beginning with the Norwood operation in the first week of life, followed by the Glenn procedure at around four to six months and the Fontan operation at around three to four years of age. This pathway results in a circulation where the single right ventricle does the work of pumping blood to the body, while blood flows passively to the lungs. Dr Giardini leads the specialist single ventricle survivorship programme at Great Ormond Street Hospital and has particular expertise in the long-term care of these patients.
Pulmonary atresia means the pulmonary valve has not formed, so there is no direct connection between the right ventricle and the lungs. Blood can only reach the lungs through alternative pathways, such as the ductus arteriosus or collateral blood vessels. The treatment depends on whether the right ventricle is of adequate size (pulmonary atresia with intact ventricular septum) or is associated with a VSD and abnormal lung blood supply (pulmonary atresia with VSD and major aortopulmonary collateral arteries). Some babies can undergo catheter-based opening of the pulmonary valve, while others need surgical repair, sometimes in multiple stages.
Total anomalous pulmonary venous drainage (TAPVD) is a condition in which the veins carrying oxygen-rich blood from the lungs connect to the wrong part of the heart (usually the right atrium or a systemic vein) rather than to the left atrium where they should drain. This means oxygen-rich blood mixes with oxygen-poor blood and the circulation is inefficient. If the drainage pathway is obstructed, TAPVD is a surgical emergency. Surgical repair reconnects the pulmonary veins to the left atrium and results are generally very good.
Tricuspid atresia means the tricuspid valve (the inlet valve to the right ventricle) has not formed. Blood cannot flow normally from the right atrium to the right ventricle, and the right ventricle is typically small. Babies survive because blood mixes through a hole in the atrial septum and reaches the lungs through a VSD or the ductus arteriosus. Like HLHS, tricuspid atresia is managed along a staged surgical pathway leading to a Fontan circulation.
Other single ventricle conditions include double inlet left ventricle, unbalanced atrioventricular septal defect and other complex anatomies in which only one of the two ventricles is capable of supporting the circulation. All of these are managed with a staged approach towards a Fontan circulation. Dr Giardini has extensive experience in every stage of this pathway.
Severe valve obstruction in the newborn period, including critical aortic stenosis and critical pulmonary stenosis, can present as emergencies requiring urgent balloon valvuloplasty to open the obstructed valve. These are covered in detail on the aortic valve and pulmonary valve pages of this website.
In most cases, there is no single identifiable cause. The heart forms during the first eight weeks of pregnancy, and complex defects occur when this development follows an unexpected pathway. Nothing a parent did or did not do caused this, and in the vast majority of cases the condition is not preventable.
Some complex heart defects are associated with genetic conditions such as Down syndrome (trisomy 21), Turner syndrome, 22q11.2 deletion syndrome (DiGeorge syndrome) and others. Where a genetic association is suspected, Dr Giardini can arrange appropriate genetic testing and counselling. However, most complex heart defects occur in otherwise healthy babies with no family history.
Many complex heart conditions are now identified before birth, usually at the 20-week anomaly scan or through a specialist foetal echocardiogram. Prenatal diagnosis is extremely valuable because it allows delivery to be planned at a centre with specialist neonatal cardiac facilities, ensures that the medical team is prepared to provide immediate care after birth, and gives parents time to understand the diagnosis and ask questions before the baby arrives. Not all conditions are detectable prenatally, and some are more difficult to diagnose on foetal imaging than others, but the detection rate for complex defects has improved significantly in recent years.
After birth, complex heart conditions may be detected through newborn pulse oximetry screening (a painless test measuring oxygen levels in the blood), clinical examination, or when a baby develops symptoms such as blue discolouration (cyanosis), fast breathing, poor feeding, unusual drowsiness or low oxygen levels. If a heart condition is suspected, an echocardiogram performed by a specialist paediatric cardiologist provides a definitive diagnosis.
Not all babies with heart conditions show obvious signs immediately, particularly if the ductus arteriosus (a normal fetal blood vessel) is still open and maintaining blood flow. When the ductus begins to close, typically in the first few days of life, symptoms of critical heart disease may emerge quickly.
Parents should seek urgent medical attention if their baby develops a blue or grey discolouration of the lips, tongue or skin, rapid or laboured breathing, sweating or distress during feeding, very poor feeding or refusal to feed, unusual sleepiness or reduced responsiveness, or a generally pale or mottled appearance. If you are concerned that something is not right, it is always appropriate to seek medical review without delay. In critical situations, a medication called prostaglandin E1 is given intravenously to reopen the ductus arteriosus and maintain blood flow to the lungs or body as a life-saving bridge while the medical team arranges definitive treatment.
Treatment depends entirely on the specific diagnosis, the anatomy of the heart and how well the baby is coping.
Some babies need urgent intervention within hours or days of birth. This may involve a catheter-based procedure (such as a balloon atrial septostomy to allow blood to mix between the upper chambers, or balloon valvuloplasty to open a critically narrowed valve) or emergency surgery. Other babies are stabilised with medication and the surgical plan is carefully developed over the following days or weeks.
For conditions that can be fully repaired, such as transposition of the great arteries or total anomalous pulmonary venous drainage, a single corrective operation may restore normal or near-normal circulation. For single ventricle conditions such as HLHS, tricuspid atresia and double inlet left ventricle, treatment follows a staged surgical pathway over the first few years of life, with each operation progressively reconfiguring the circulation.
At Great Ormond Street Hospital and the Portland Hospital, Dr Giardini works alongside one of the most experienced paediatric cardiac surgical teams in the world. Decisions about treatment are made collaboratively, with input from cardiologists, surgeons, intensivists, specialist nurses and the family. The aim is always to achieve the best possible outcome for each individual child, and Dr Giardini ensures that parents understand every step of the process clearly.
The outlook for babies born with complex heart conditions has improved enormously. Survival rates for many of the conditions described on this page now exceed 90% in experienced centres, and the large majority of children grow up to attend school normally, participate in physical activity (with appropriate guidance) and enjoy a good quality of life.
Some children will need further procedures or operations as they grow. Some will require lifelong medication, and most will need ongoing follow-up with a paediatric cardiologist through childhood and into adult life. This is not a sign that something has gone wrong; it is simply part of the long-term care pathway that ensures the heart continues to function well as the child grows and develops. Dr Giardini provides continuity of care from the newborn period through childhood and coordinates transition to adult congenital heart disease services when the time comes.
For children with single ventricle physiology and a Fontan circulation, long-term follow-up is particularly important. Dr Giardini leads the single ventricle survivorship programme at Great Ormond Street Hospital and has published extensively on outcomes in this group, helping to shape the care pathways that allow these children to thrive.
It is also important for parents to know that the emotional and psychological impact of having a baby with a complex heart condition is entirely normal and should not be underestimated. Many families benefit from speaking with specialist nurses, psychologists or other parents who have been through similar experiences. Dr Giardini's team can help connect you with the right support.
Whether your baby has been diagnosed prenatally with a complex heart condition, has presented with symptoms after birth, or you have received a diagnosis and would like a second opinion, Dr Giardini can provide a comprehensive assessment with same-day appointments and a clear, jargon-free explanation of the diagnosis, treatment options and outlook. He is frequently sought for second opinions by families and clinicians both within the UK and internationally.
Congenital heart defects affect approximately 1 in 100 babies. Complex or critical conditions are less common, accounting for around a quarter of all congenital heart defects, but they are well recognised and routinely managed in specialist centres with excellent outcomes.
Yes. Many complex heart defects are identified during the 20-week pregnancy scan or through a specialist foetal echocardiogram. Prenatal diagnosis allows delivery to be planned at a specialist centre and ensures the team is prepared to provide immediate care.
No. In the vast majority of cases, there is nothing a parent did or could have done differently. Complex heart defects develop during the earliest weeks of pregnancy and are not preventable.
Many babies with complex heart conditions do need surgery, sometimes within the first days or weeks of life. The type and timing of surgery depend on the specific diagnosis. Dr Giardini will explain the treatment plan clearly and ensure you understand what to expect at each stage.
Survival rates have improved dramatically. For many conditions, including transposition of the great arteries, survival in experienced centres exceeds 97%. Even for the most complex conditions such as hypoplastic left heart syndrome, outcomes continue to improve with modern surgical techniques and specialist care.
In some heart conditions, only one of the two ventricles is capable of doing the pumping work. Treatment involves a staged series of operations that eventually create a Fontan circulation, where the single ventricle pumps blood to the body and blood flows passively to the lungs. Dr Giardini has extensive experience in looking after children with single ventricle and Fontan surgery.
Many children with complex congenital heart disease lead full, active lives. They attend school, participate in sport (with appropriate guidance) and enjoy a good quality of life. Some require ongoing follow-up and medication, but this is a well-established part of the care pathway.
Yes. Most children with complex heart conditions benefit from regular cardiology review as they grow, even after successful treatment. This ensures the heart continues to function well and any late issues are detected and managed early.
If you feel uncertain about a diagnosis or treatment plan, or simply want reassurance from another specialist, a second opinion is always appropriate. Dr Giardini is frequently sought for second opinions and welcomes families who want clarity and confidence in their child's care.
If a heart condition has been suspected during pregnancy, if your baby has symptoms after birth, if a murmur has been detected, or if you have an existing diagnosis and want a clear explanation of what it means, specialist assessment is recommended. Dr Giardini provides same-day echocardiography and immediate results at his London clinics.
Author: Dr. Alessandro Giardini, MD, PhD
Written 03/04/2026