Blockages of blood vessels to the heart are the most common cause of chest pain and heart attacks. Doctors typically diagnose these blockages by using stress tests and angiography. With stress tests, people run on a treadmill or are given medicine to increase the stress on their heart. Doctors then take pictures of the heart's blood flow to see whether it is abnormal. With angiography, doctors put a catheter into the heart, squirt dye into its vessels, and take x-rays to see the blockages. Angiography is more accurate than stress testing but is invasive, expensive, and occasionally harmful. Recently, computed tomography (CT or “CAT”) scans have been developed that can take pictures of the blood vessels in the heart (CT coronary angiography or CTCA). These scans are noninvasive, less expensive, and less harmful than standard angiography, but not a lot is known about their accuracy or how they should be used in comparison to standard testing.