A sestamibi, or MIBI, nuclear stress test is an imaging test done to determine the efficiency of blood flow into the cardiac muscles when the heart is both active and at rest, notes MedlinePlus. The test checks if there is enough oxygen and blood supply to a stressed heart.
During a MIBI stress test, a doctor first injects a radioactive substance into a patient's vein, after which the patient lies down for 15 to 45 minutes, explains MedlinePlus. The doctor observes how the blood transports the substance to the heart with a special camera. The patient then walks on a treadmill to speed up the heartbeat and blood pressure, and his heart rhythm is observed. The doctor administers the radioactive substance again, and the patient waits for an additional 15 to 45 minutes. Finally, the doctor scans the heart with the camera again.