“As she was getting ready for bed, a 52-year-old woman noticed a familiar squeezing or tightness in the middle of her chest. She had experienced cardiac problems in the past and felt this was a resurgence of her angina, so she took a sublingual nitroglycerin tablet. It burned underneath her tongue, yet provided no relief for her chest discomfort. In the next half hour, she took two more sublingual nitroglycerin tablets. The pain, rather than abating, started to radiate toward her back, which concerned her enough to call for help.”