Among sudden deaths, patients with coronary heart disease combined with acute heart attack are the most common. However, many patients in the clinic have no obvious symptoms before the onset of the disease, which leads to death due to delayed consultation. People may ask: Isn’t an acute heart attack a “dying” chest pain, but why is there no such symptom? The heart is an organ that feels pain, but why does it not send a “signal” when something is wrong? Modern medical research shows that this is due to a malfunctioning heart pain alarm system. This is most often due to the following: First, the heart is sensitive to pain in different ways depending on the location of the heart lesion. If the lesion is in the right coronary artery, it is not very sensitive to pain; some are posterior wall myocardial infarction, which may also not appear pain; some subendocardial myocardial damage, no pain sensation. Second, individual differences are not the same for pain sensitivity. For example, the elderly have poor sensitivity to pain, mainly because of the aging of organs and systems throughout the body, so they feel sluggish and less sensitive to pain; plus there is brain atrophy or dementia, which leads to a decline in language expression, so they cannot say a thing, which masks the condition. Third, painless heart attack. This type of acute infarction is mostly seen in elderly patients with diabetes combined with coronary artery disease, because the coronary artery lesions caused by diabetes often involve multi-level vessels, which can range from the coronary artery trunk to the tiny arteries, while the lesions of general coronary artery disease are mainly in the coronary artery trunk or large branches, and less often involve the small arteries or micro arteries. This kind of acute heart attack is much more serious than general patients because of the wide range of lesions, myocardial ischemia, injury and necrosis, plus diabetic patients often have peripheral neuropathy, their plant nerve function is impaired, sensory nerve involvement, it will make the pain sensation become dull or even no pain sensation. Fourthly, it is related to emotional changes, such as excessive stress and fatigue, which can make patients less sensitive to pain and become sluggish. It is worth to be alerted that painless heart attack is much more serious than general heart attack, and some patients have shock, acute heart failure, or even sudden death at the beginning of the attack. Therefore, painless heart attacks should not be taken lightly.