I recently had a cardiac stress test. It was my fourth. Its purpose was to determine whether my heart is pumping an adequate quantity of blood during exercise. Additionally, is there a partial arterial blockage or damaged heart muscle? The test involves the patient receiving an injection of Cardiolite[R], a substance containing a molecule to which Technetium-99m (Tc-99m) is attached, and then lying under a camera that detects gamma rays emanating from the interior heart wall and forms an image indicative of blood flow in the resting heart. This is followed by treadmill exercise, another injection of Cardiolite[R] during peak exercise, and then another image obtained with the camera indicating maximum blood flow. After the test, I decided to determine the biological half-life of Cardiolite[R].