A normal ejection fraction is around 55 to 75%. That fraction indicates the percent of blood pumped out the left ventricle into circulation with each hearbeat. There is a deificiency represented by the 30% EF.
If the blood flow to the heart muscle is impeded, the heart muscle cells (myocytes) can not be energized (repolarized) resulting in a failure to contact and pump sufficient blood to meet the system's demand for blood/oxygen. Obviously, there are some cells that function properly getting enough blood/oxygen, but the area that is deficit requires a bypass.
There is medication to increase contractions, regular exercise (aerobic) can increase the strength of the viable muscle cells. Sometimes heart cells are hybernating and when supplied with sufficient blood flow can return to normal functionality.