mitral regurgitation (mr) "decreases" afterload. in ventricular systole under mr, regurgitant blood flows backwards/retrograde back and forth through a diseased and leaking mitral valve. the remaining blood loaded into the lv is then optimally ejected out through the aortic valve. with an extra pathway for blood flow through the mitral valve, the left ventricle does not have to work as hard to eject its blood, i.e. there is a decreased afterload. afterload is largely dependent upon aortic pressure.