Magnetic Resonance Angiogram (MRA)
An noninvasive test that combines the injection of dye into the venous system with the use of radio waves and magnetic fields, to define the anatomy of the vessels in the body, thus creating a three-dimensional image.

Magnetic Resonance Imaging (MRI)
A noninvasive test that creates images by using radio waves and strong magnetic fields to visualize the soft tissues or bones of the body. It creates a three dimensional image.

MAZE
A surgical intervention aimed at relieving atrial fibrillation (rapid quivering of the heart's upper chamber).

Mechanical Valve
A heart valve that has been manufactured by artificial means. Blood thinners are usually required after implantation.

Mitral Valve
One of four valves in the heart, located between the left atrium and the left ventricle. It is the only natural bicuspid (two leaflet) heart valve.

Myocardial Infarction (MI)
An irreversible injury to the heart muscle, also known as a heart attack. If blood flow is cut off to a portion of the heart , it can cause tissue death in that area due to lack of oxygen.