Patients are advised to fast before doing coronary CT examinations. It is often necessary to use contrast agents when doing coronary CT examinations, and contrast agents can easily cause allergic reactions, which can lead to a series of symptoms such as nausea, vomiting, generalized hives, etc. Severe cases can lead to death due to anaphylaxis. If the patient does not fast, the allergic reaction to the contrast agent will induce nausea and vomiting, which can lead to aspiration, and in serious cases, suffocation, affecting life, so the day before the coronary CT at least twelve hours of fasting to ensure gastric emptying, so that the coronary CT examination is more safe and reliable, you can eat antihypertensive or heart rate stabilizing drugs, just can not eat.