 So, the final group in the four chamber view is the septal defects and the crux of the heart and I am mostly going to focus on the AV septal defect. And I will also show you CCTDA4 chamber view because it is very deceptively looks very normal. So, this is an example of a complete AV septal defect when you look at the center portion of the heart you can make out the defect. So, let us see what are the components of the complete AV septal defect. The first is that there is a large defect in the crux of the heart there and this is a frame where the valves are open it is a diastolic frame and you see a large defect in the crux of the heart with the valves open. So, that is the first clue. So, it is as if there is a whole the entire central portion of the heart where the atrial and ventrillate at the meat it is punched out. The second feature normally we know that when you insist to leave and the valves are closed there is a normal phenomenon called offsetting where the tricostate valve is at a lower level compared to the mitral valve. In AV septal defect there is a linear insertion of the atrial ventricular valves and there is complete loss of offsetting. The third feature is that the atrial ventricular length ratio normally the ventricular length will be more than the atrial length while in AV septal defect there is a downward displacement of the valves. So the ventricular AV length ratio will be increased that is the third feature. And the fourth feature is when you put colour you find a single channel of blood flow into the ventricles. Once instead of two separate channels of colour flow you see a single channel blood flow and as we can see in this movie you can also make out some atrial ventricular valve regurgitation. So the two important imaging points for AV septal defect are in diastole frame you find a large defect in the centre of the heart, the crux of the heart and in the systolic frame you see loss of offsetting or the linear insertion. Now the entity which I showed you was what is called a balance type of AV septal defect where the two ventricles were equal sized. Now look at this type of AV septal defect. Here you see that the valve is predominantly opening into the right ventricle which is a large ventricle while the ventricle on the left side is really small. This should not be termed as hyperplastic left heart syndrome that is wrong. This should be termed as unbalanced type of AV septal defect with a small lv. This is not left heart hyperplasia and if you write it in anatomical sense you may be okay. You are seeing a small lv but that is not a correct diagnosis. So please do not label this condition as hyperplastic left heart syndrome. I have seen several reports where unbalanced AV is reported as hyperplastic left heart syndrome. So it's a wrong terminology so the correct terminology is unbalanced type of atrial septal defect with small lv. This is often a part of an entity called right isomerism which is you see. Now this is another type of AV septal defect. You see two good size ventricles but you see how slow the heart rate is. So this is typically the type of AV septal defect which is found in left isomerism. Often has associated with complete heart block. See here on the other picture you see here a very interesting finding. You see two vessels instead of one where the descending aorta is. This is called a double vessel sign. One of this is the aorta and the second is dilated as they go away. And this is because the inferior vena cava is interrupted here. So this is the hallmark of what is called left isomerism. So a very deceptive looking picture looks like AV septal defect but you have this double vessel sign. Immediately you diagnose left isomerism or heterotaxi. So unbalanced AV septal defect and the AV septal defect with double vessel sign of radicardia is a part of heterotaxis type syndrome. The prognostic importance is that these entities are not associated with down syndrome. So you do not need to do a carotid typing for this condition. However, a balanced AV septal defect has a 50% association with trisomy 21 or down syndrome. So that is where you would do a amniose endosynthesis and carotid typing. So it is very important to distinguish between AV septal defect occurring in different settings. So I am not showing the full cases all the pictures because I do not like to do that because I try to stick to the topic which we are discussing which is AV septal defect. So please distinguish between the AV septal defect which you find in trisomy 21 which is a balanced AV septal defect with equal size ventricles versus the AV septal defect which is seen in isomeric hearts or heterotaxi in which either you get an unbalanced AV septal defect or you get a picture like this where you have the interrupted IVC with AV septal defect as shown by the double vessel sign.