Heart valves are one-way pass for blood to pass out of chamber into another lower chamber and then a valve opening for blood to go into circulation. When the valve is not compliant it usually due to leaflest that tightly cover the opening and blood flows back into a chamber and the backflow is referred to as regurgitation. MR refers to the mitral valve and one of the leaflets does not close off the back flow. The degree of backflow and location is correlated to the height and direction of the jet stream.
Mild, trivial, trace of regurgitation is not considered medically significant and almost always does not progress or cause any symptoms. Mild to moderate may require watching but should not cause any symptoms. Left ventricle (LV) pumping capacity is good and contractility is sufficient to provide adequate blood flow to the body. Right ventricle pumps blood to the lungs to be oxygenated and that is good as well.
AR is aorta valve regrugitation.
TR is the right side valve
MR is mitral valve regurgitation.
Hope this helps put the issues into a perspective for you. Thanks for your questions and if you have any further questions or comments you are welcome to respond. Take care.
Ken