**3. Anatomy**

Even though VSDs are encountered on a day to day basis by cardiologists and cardiovascular surgeons alike, its classification and nomenclature continues to remain variable among different groups. Two famous schools of thought come from descriptions by Soto et al. [9] and Van Praagh et al. [10].

Soto et al., broadly divided the ventricular septum into the membranous and muscular portions. The membranous septum is separated by the septal leaflet of

*Ventricular Septal Defects: A Review DOI: http://dx.doi.org/10.5772/intechopen.104809*

tricuspid valve tissue into atrioventricular and interventricular components. The muscular septum in turn is described as having three different components, (**Figure 1**): The inlet muscular septum is small and divides the mitral and tricuspid valves. The trabecular septum is the largest portion of the ventricular septum extending to the ventricular apex. The infundibular septum is the portion above the crista supraventricularis that separates the aortic and pulmonary valves. The other part of the crista is between the tricuspid and pulmonary valves [11].

Van Praagh and associates have described these defects as atrioventricular canal, muscular, conoventricular, and conal septal type ventricular septal defects.

Accordingly, the ventricular septal defects may be classified as follows: (**Figure 2**).


**Figure 2.** *Types of ventricular septal defects by location.*

it is more common among Asians with reported incidence up to 30% in Japanese population.

D. Atrioventricular septal defects are located in the inlet septum and will not be reviewed in this chapter.

VSDs are also classified based on their size: those less than one-third (~33%) the size of the aortic valve annulus are considered as small; more than half (50%) as large and moderate being in between.
