Generally speaking, winter is the season of high incidence of coronary  heart disease (CHD) and cerebrovascular disease. However, according to clinical  research, people tend to get CHD easily in summer. Here are the reasons for the  high incidence of CHD in summer. 1. The weather in summer is sultry and the air  is humid, so people’s blood vessels get dilated, increasing the blood flow of  the limbs and reducing the amount of blood returned to the heart, resulting in  myocardial ischemia. In summer, the days are longer than nights. The middle-aged  and elderly people are irritable and hard to fall asleep, resulting in  insufficient sleep. Due to the long light period in summer, the pineal gland of  human thalamus is in a state of shutdown for a long time during the day,  resulting in a decrease in the secretion of melatonin (MT) known as a sleep  messenger, causing changes in the circadian clock rhythm and insomnia. In  addition to controlling the circadian clock to start sleep, MT can also remove  free radicals and maintain cardiovascular system. Due to the decline of MT  secretion in summer, free radicals in the body cannot be cleared in time,  causing coronary heart disease. In the case of high temperature in summer, lack  of sleep can cause sympathetic nerve excitement, causing accelerated heart rate,  blood vessel contraction, and high blood pressure. At the same time,  irritability and sweating may result in a large amount of fluid loss, causing  thick blood and blockage of the heart and brain blood vessels and insufficient  coronary blood supply. In summer, the high temperature and humidity lead to low  oxygen content in the air, and it is easy to cause myocardial hypoxia, which  leads to heart disease. The typical symptom of coronary heart disease is chest  pain, which may be accompanied by breathing difficulty, nausea, and sweating.  This symptom may last for a few minutes. What can be relieved within fifteen  minutes is often angina. If there is still no relief after more than 30 minutes,  it might be acute myocardial infarction. The patient should be treated in a  professional hospital as soon as possible. People who have been identified as  high-risk or coronary heart disease need to carry nitroglycerin with them, which  can be used to relieve chest pain. If one piece does not relieve the symptoms,  the patient could take another one, but the limit is three. If it is still not  effective, you should call 120 as soon as possible for professional help. Once  there is symptom, you should stop exercising, take some rest and wait for the  ambulance, and go to the hospital in time.