>> reporter: it is often women? >> typically women. a big problem. >> reporter: as many as 100,000 women have suffered a heart attack that went undiagnosed. the study helps explain why. often when a man has a heart attack it is because of a severely blocked artery, angiogram, the common test can easily spot this blockage. but heart attacks can also occur particularly in women when plaque builds up along the artery wall but the artery itself remains open. that plaque can cause a deadly clot. but an angiogram doesn't catch this build-up. look at carolyn's angiogram. >> these arteries are wide open. >> reporter: when doctors used an intravascular ultrasound to look inside her arteries they spot the trouble. but not all hospitals have this kind of test available. so if a woman who suffered symptoms of a heart attack they should question their doctor before going home without treatment. >> am i getting every proven medicine that would prevent me from having a heart attack. >> reporter: patients should ask for the test proving to catch