Lactate Dehydrogenase (LDH) is an enzyme which plays an important role in making your body's energy. It is found in almost all the body's tissue, including those in the blood, heart, kidneys, brain, and lungs. When these tissues are damaged, they release LDH into the bloodstream or other body fluids. If your LDH blood or fluid levels are high, it may mean certain tissues in your body have been damaged by disease or injury.