A client arrives in the emergency department reporting crushing substernal pressure that started forty minutes ago while shovelling snow. The pressure radiates to the left jaw, and the client is diaphoretic, nauseated, and says "something is very wrong." Nothing about that presentation is subtle, and it is also not the presentation you will most often miss. The client you will miss is the seventy-eight-year-old woman with diabetes who reports only unusual fatigue and indigestion, or the postoperative client whose only complaint is new shortness of breath. Acute coronary syndrome is the umbrella term for the spectrum of conditions caused by a sudden reduction in blood flow through a coronary artery. It spans unstable angina, non-ST-elevation myocardial infarction, and ST-elevation myocardial infarction. What separates them is not the underlying event — all three begin with the same disrupted plaque — but how completely the artery is blocked and whether heart muscle has actually died. For the nurse, the value of understanding acute coronary syndrome is not in naming the subtype. It is in recognizing that a specific window of time is...