Mitral regurgitation is much more common than aortic regurgitation. When the valve leaks, the heart has to work a lot harder to pump enough blood in a forward direction. Because the heart is a muscle and - like any other muscle in your body - is designed be able to do extra work. But in order for your brain and the rest of our body to get an adequate supply, your heart has to pump harder to move the blood forward and make up for the blood that is flowing back into the chamber.
It is possible to have significant leaks in a valve and still feel absolutely fine. However, enlargement of the heart can eventually lead to heart failure. In most cases, a regurgitating valve can be successfully treated.