Chelation therapy is a process involving the use of chelating agents to remove heavy metals from the body. For the most common forms of heavy metal intoxication, those involving lead, arsenic or mercury, the standard of care in the US dictates the use of DMSA.
EDTA treatment has been around since the 1940's, when it was developed to treat lead poisoning.
Chelation is a chemical process in which a substance is used to bind molecules, such as metals or minerals, and hold them tightly so that they can be removed from a system, such as the body. In medicine, chelation has been scientifically proven to rid the body of excess or toxic metals. For example, a person who has lead poisoning may be given chelation therapy in order to bind and remove excess lead from the body before it can cause damage.
In the case of EDTA chelation therapy, the substance that binds and removes metals and minerals is EDTA (ethylene diamine tetra-acetic acid), a synthetic, or man-made, amino acid that is delivered intravenously (through the veins). EDTA was first used in the 1940s for the treatment of heavy metal poisoning. EDTA chelation removes heavy metals and minerals from the blood, such as lead, iron, copper, and calcium, and is approved by the U.S. Food and Drug Administration (FDA) for use in treating lead poisoning and toxicity from other heavy metals. Although it is not approved by the FDA to treat CAD, some physicians and alternative medicine practitioners have recommended EDTA chelation as a way to treat this disorder.

EDTA chelation therapy and side effects:
When used as approved by the FDA (at the appropriate dose and infusion rate) for treatment of heavy metal poisoning, chelation with EDTA has a low occurrence of side effects. The most common side effect is a burning sensation experienced at the site where the EDTA is delivered into the veins. Rare side effects can include fever, hypotension (a sudden drop in blood pressure), hypocalcemia (abnormally low calcium levels in the blood), headache, nausea, vomiting, and bone marrow depression (meaning that blood cell counts fall). Injury to the kidneys has been reported with EDTA chelation therapy, but it is rare. Other serious side effects can occur if EDTA is not administered by a trained health professional.