Seem’s like no one wants to answer your question. I’m assuming that you already know that the mitral valve has 2 cusps and the tricuspid valve has 3 cusps and really your question is either “why did god make the mitral and tricuspid valves the way they are,” or “what is the evolutionary/practical significance of having a 2 cuspid valve on the left side and a 3 cuspid valve on the right side. It’s actually a very interesting question, and I posted a link that tries to answer your question: http://www.madsci.org/posts/archives/1997-03/855255174.An.r.html#conclusion I’ll do my best at summarizing below. During embryological development, while the heart is still being formed, there are a number of unique features.. 1. There a direct communication between the right and left atrium (foramen ovale). This allows placental oxygenated blood to directly enter the left side and then to the rest of the body. 2. During development, there is no barriers between the atria and ventricles. Rather, the c