**3. Pathology**

In a normal heart, tricuspid and mitral valve annuli are positioned at different levels because of the atrioventricular septum. In AV septal defects, tricuspid valve annulus is located more apically in relation to mitral valve. The portion of the offset between tricuspid and mitral valve is the location of atrioventricular septum. It has overlapping atrial and ventricular walls [7]. Aortic valve is located anterior and superior between tricuspid and mitral valve, what is referred to as wedged between these valves. This makes the subaortic outflow region placed in between tricuspid and mitral valves. The papillary muscles in the left ventricle are located antero-superior and postero-inferior region. Another feature of importance to this topic, the distance from mitral valve to apex of left ventricle is same as the distance from left ventricular apex to aortic valve (**Figure 3**).

In patients with AV septal defect, the fundamental abnormality is absence of the atrioventricular septum or having a common atrioventricular junction. This results in a cascade of features that are different from normal hearts. The common features shared by all forms of atrioventricular septal defects are:

a.Presence of common atrioventricular valve

b.Elongation of the left ventricular outflow tract

*DOI: http://dx.doi.org/10.5772/intechopen.105615 Atrioventricular Septal Defects*

#### **Figure 2.**

*Fetal echocardiogram four-chamber view: Complete AVSD. RA, right atrium; LA, left atrium; RV, right ventricle; LV, left ventricle. \*Primum atrial septal defect and inlet ventricular septal defect.*

#### **Figure 3.**

*2D echocardiogram parasternal long axis view: A. In normal cardiac anatomy, distance from the mitral valve to left ventricular (LV) apex and from LV apex to aortic valve is same. B. In AVSD, LVOT is elongated and distance from LV apex to left AV valve annulus is shorter. LA, left atrium; RV, right ventricle; Ao, aorta.*

