There are quite a number of congenital heart defects (CHDs) that children may be born with. Some of these are of trivial nature while others are quite severe and significant. All these malformations can be categorized into several groups. This categorization takes into account the type of defect or defects and the variety of disturbances these impose on the functioning of the heart. This type of differentiation is important in decision making procedures as to the type of treatment required and the exact timing of the selected procedure. Some minor malformations do not require major interventions while other more severe ones may even threaten life and need urgent treatment. In some, it is possible to wait and undertake corrective measures as a well planned and elective procedure. All this depends on an accurate assessment of the type and severity of the defect.

One type of congenital cardiac malformations is reflected by some sort of obstruction to the flow of blood in some area of the heart or in one of the major blood vessels that leave the heart. Obstructive defects occur when heart valves, arteries or veins are either abnormally narrowed or completely blocked. Common obstructive defects include pulmonary valve stenosis, aortic valve stenosis, and coarctation of the aorta, with other types such as bicuspid aortic valve stenosis and subaortic stenosis being comparatively rare. Any narrowing or blockage can cause heart enlargement, more specifically in the chambers that are just behind the obstruction. This occurs as a result of those chambers being called upon to perform extra work to pump blood against the obstruction imposed by the narrowed area. If this state of affairs is allowed to go on for long enough the end result is the failure of that part or the particular chamber of the heart. One particular malformation, coarctation of the aorta is a narrowing of a portion of the aorta which often seriously decreases the blood flow from the heart out to the lower portion of the body. This condition is associated with high blood pressure in the arms and low blood pressure in the legs. It is an eminently treatable malformation.

Three extreme forms of obstructions merit special mention. One is pulmonary atresia. In this condition, the pulmonary valve and the pulmonary artery which is the main large vessel that takes blood from the right ventricle to the lungs does not develop or is completely narrowed and blocked. The second is tricuspid atresia in which the tricuspid valve that separates the right atrium from the right ventricle is undeveloped and completely obstructed. The last one is failure of development of an entire side of the heart. This is known as under development or hypoplasia and it can typically result in the failure of either the right ventricle or the left ventricle to develop adequately, leaving only one side of the heart capable of pumping blood to the body and lungs. Under development or hypoplasia of the heart is rare but is the most serious form of CHD. When it affects the left side it is called hypoplastic left heart syndrome and when the right side is involved it is known as the hypoplastic right heart syndrome. In both conditions, the presence of an added shunt to allow blood to be circulated is essential to the infant’s ability to survive until emergency heart surgery can be performed. Indeed, without such an added abnormal communication, the baby will not survive as blood cannot circulate to the body or to the lungs, depending on which side of the heart is defective and hypoplastic.

Another group of congenital cardiac malformations consist of abnormal communications between certain regions of the heart which allows unusual shunting of blood. Some of these are due to septal defects and are colloquially known as "hole-in-the-heart" conditions. The septum is a wall of tissue which separates the left heart from the right heart. It is comparatively common for defects to exist in the inter-atrial septum or the inter-ventricular septum, allowing blood to flow from the left side of the heart to the right thereby reducing the heart’s efficiency. Ventricular septal defects (VSDs) are collectively the most common type of CHDs, although approximately 30 per cent of adults have a type of small atrial septal defect (ASD) called patent foramen ovale. A VSD is a hole in the wall or septum between the heart’s left and right ventricles. These can occur at different locations and vary in size from very small to very large. Some of the smaller defects may gradually close spontaneously with the growth of the child. Septal defects or holes-in-the-heart are probably the defects that are most familiar to the non-medical persons.

Septal defects may or may not cause a bluish discolouration of the nail beds, lips and peripheries. Such discolouration is known as cyanosis and its onset and progression depends on the severity of the defect and the direction of flow through the defect. Cyanosis occurs when there is mixing of blood from the right to the left side through the shunt. An important shunt also occurs due to the persistence of a primitive connection from the aorta to the pulmonary artery that is present in fetal life. This connection, known as the ductus arterriosus, performs an important function during fetal life. It is a normal blood vessel in the developing fetus that diverts circulation away from the lungs and sends it directly to the body as the lungs are not used while the unborn fetus is in amniotic fluid and it gets oxygen directly from the mother’s placenta. The ductus usually closes on its own shortly after birth as it is no longer needed once a newborn breathes on his or her own. If the ductus fails to close, then a condition called persistent ductus arteriosus (PDA) results, which can result in too much blood flow to a newborn’s lungs. PDA is common in premature babies.If large enough, this could cause major problems, especially in early life. Even when the initial defect leads to left to right shunting at the start, this may get reversed and lead to a right to left shunt as time goes by. This is due to the pressures within the right side of the heart increasing to a level that overrides the pressures in the left side of the heart. The appearance of cyanosis in such a situation is of ominous significance. The appearance of cyanosis in such a situation also means that the condition has progressed beyond redemption and it is not possible to correct the problem surgically.

A whole separate group of malformations of varying sizes and shapes is associated with cyanosis from the outset. This bluish tinge in the peripheral tissues is due to deoxygenated blood mixing with the oxygenated blood that is pumped to the peripheral tissues. It simply means that whatever the malformation is, there is concomitant shunting of blood from the right side of the heart to the left side of the heart after the blood traverses the circulation through the lungs. In most malformations of this nature, either there is an atrial or ventricular septal defect through which the blood is shunted or there is a persistent ductus arteriosus with a reversed shunt or there is a positional change in the great vessels so that blood from the right side of the heart enters the left side, most of it virtually by-passing the lungs. There are complex combinations of defects in these conditions and specified combinations are given explicit names such as Fallot tetrology, transposition of great arteries, truncus arteriosus, single ventricle, atrio-ventricular canal defect, total anomalous pulmonary venous connections etc. These are all rather esoteric and severe malformations which would need complex cardiac surgery for their correction. Some of them present with major problems at birth and the newborn babies with these defects are quite ill with the effects of the malformations. They generally need some form of interventional or surgical management to survive. Others take a little time to show the full spectrum of clinical features. One such example is Fallot tetrology. However, one thing is absolutely certain about this group of conditions. None of them ever resolve spontaneously. In some of these complex malformations all kinds of defects may occur. Quite a few of these are not known associations and do not fit into a well known and previously described group of conditions or syndromes. Fairly often, unexpected combinations of malformations are found in some of these children. This makes it even more important to delineate the exact defects accurately.

Paediatric cardiology and modern paediatric cardiac surgery have developed and progressed rapidly and perhaps unbelievably over the last few decades. It is possibly true to say that these highly specialized fields have taken a quantum leap of progress during the last couple of decades. Some congenital cardiac defects which were considered to be inoperable and irremediable in the not too distant past can now be dealt with using highly sophisticated modern technology. Frustration and despair of parents with children suffering from some severe cardiac malformations are being rapidly ameliorated by the amazing results of some innovative procedures undertaken by highly skilled doctors working in these fields. However, and most unfortunately, still there are some extremely complicated defects for which curative procedures are not available. For them, heart transplants remain the only feasible remedy for the condition.

In the light of the above narrative, it is vitally important to make a definitive, complete and accurate diagnosis of the structural and anatomical defects that are found in any congenital cardiac malformation. All investigations are geared towards this inescapable goal. Before any corrective intervention is undertaken, it is essential to know the absolutely exact types and extent of the malformations. Treatment could be rationally planned and undertaken only when such exacting details are available. Interventional cardiologists and cardiac surgeons need to be supplied with the exact details of the malformations prior to embarking on a planned course of management. It is not at all pleasant for such a practitioner to be confronted with unexpected and previously undiagnosed malformations in the middle of an interventional procedure or open cardiac surgery. Clinicians entrusted with the task of making a definitive diagnosis would even go that extra mile to make absolutely sure that all abnormalities are accounted for in a given child with any type of congenital cardiac malformations.