Chelation therapy consists of bonding a toxic metal atom, such as lead, to a ligand (a “tie in”) molecule. In fact putting the dangerous metal in quarantine.
Why and when would we want to bind a metal?
“…Chelation therapy is the use of chelating agents to detoxify poisonous metal agents such as mercury, arsenic, and lead by converting them to a chemically inert form that can be excreted without further interaction with the body…”
So chelation is used primarily to bind and remove toxic metals located throughout the body
The American Cancer Society has the following entry on chelation therapy :
“…Chelation therapy has also been promoted as an alternative treatment for many unrelated conditions, such as gangrene, thyroid disorders, multiple sclerosis, muscular dystrophy, psoriasis, diabetes, arthritis, Alzheimer’s disease, and the improvement of memory, sight, hearing, and smell…”
Let us look at the method as applied to heart disease
What toxic metals or minerals is this chelation process supposed to remove to fight coronary disease?
Mostly calcium: the clinical trial of the TACT study says [2,3]:
“…EDTA chelation therapy involves repeated administrations of a synthetic amino acid to reduce atherosclerotic plaque and other mineral deposits throughout the cardiovascular system…’
The plaque component with metal properties is the extracellular calcium deposits between the muscular wall and outer portion of the plaques. So Calcium seems the primary removal target.
Sure enough, an article in biomedcentral  has : “…calcium chelation resulting in dissolution of atheromatous plaques, free radical scavenging action, reduction of total body iron stores, cell membrane stabilization, arterial dilatation due to calcium channel blocking action, improvement of arterial wall elasticity and increased production of nitric oxide…”
The problem is that the chelation of calcium is not an easy process: “…the inability of EDTA, a water soluble compound, to effectively complex with plaque calcium…”
But more minerals are gathered (chelated) besides calcium:
“…Calcium disodium 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. Rather than testing calcium disodium EDTA, TACT used another salt, disodium EDTA, under an FDA license as an investigational new drug (IND). Although disodium EDTA is not approved by the FDA to treat CHD, some physicians and alternative medicine practitioners have recommended its use in chelation as a way to treat CHD…”
Here lies the main issues: iron, copper, and calcium are not necessarily bad for the body.
As a matter of fact, not enough iron is called anemia! Other risks of chelation therapy are also serious:
“…heart failure, a sudden drop in blood pressure, abnormally low calcium levels in the blood (hypocalcemia), permanent kidney damage, and bone marrow depression (meaning that blood cell counts fall)…” Also, not enough calcium is called hypocalcemia and can lead to convulsions, arrythmias, tetany and numbness/parasthesias (Wikipedia)
The figure below shows the EDTA compound binding a metal atom.
So before we remove metals and minerals indiscriminately from the body of a Cardiovascular Disease (CVD) patient, maybe we should know more about the relationship between those minerals and CVD .
But the chelation proponents argue that many other metals and minerals removable by chelation are bad for your heart. In fact, the British Medical Bulletin  adds cadmium and mercury to the list.
Essentially, heavy metal pollution is bad for you and your heart. Fine, but does that mean that most heart diseases are caused by such pollution?
That remains to be shown. Chelation seems like a dragnet removal of many metals from the CVD patient. Maybe future studies should discover a chelating agent specialized in removal of a specific metal, say, calcium.
Until then, you will note that the in the clinical trials described in 
“…A typical protocol might consist of 30 intravenously administered solutions of 3 grams of disodium EDTA with concomitant administration of varying levels of ascorbic acid, B-vitamins, heparin, and the minerals magnesium, copper, zinc, selenium and manganese delivered over 1.5 to 3 hours in 500 ml to 1000 ml of normal saline…”
The addition of minerals magnesium, copper, zinc, selenium and manganese is probably there to compensate for the removal of these essential metals from the patient’s body.
Other medications, such as diuretics can bring about loss of electrolytes and can require mineral supplementation, but the mechanics of the use of diuretics and their efficacy is well understood.
Note that heavy metal pollution has been associated with all sorts of ills , which explains the range of disease it is deemed to heal 
Coming back to heart disease, the latest results of the Trial to Assess Chelation Therapy (TACT) discussed in  are intriguing.
Quoting  : “…The primary endpoint of the trial– the composite of death, MI, stroke, coronary revascularization, or hospitalization for angina– was significantly lowered in the chelation group: 26.5% in the chelation group versus 30% in the placebo group…”
But, although 26.5% is an improvement over than 30%, it is certainly not dramatic!
Results were better, though, for diabetic and myocardial infarction subgroups, with close to 40% less risk than with the placebo. But the reason for these subgroups’ better results is not yet understood.
So let us look for more chelation studies confirming the benefits and shedding light on the processes, before jumping on the chelation bandwagon!
The problem with this sort of conclusion, is that very sick people cannot wait
But “Caveat emptor”: Enter gingerly!
- American Cancer Society ; “Chelation Therapy” ; 2008
- cardiobrief ; “NIH Trial Gives Surprising Boost To Chelation Therapy” ; Nov 2012
- clinicaltrial.gov ; “Trial to Assess Chelation Therapy (TACT)” ; Oct 2012
- biomedcentral ; “EDTA chelation therapy for cardiovascular disease: a systematic review” ;2005
- National Heart Lung and Blood Institute (NHLBI) ; “Questions and Answers: The NIH Trial of EDTA Chelation Therapy for Coronary Heart Disease” ; 2012
- British Medical Bulletin ; “Hazards of heavy metal contamination” ; 2003