Acute myocardial infarction often develops from angina pectoris. When angina persists for more than 30 minutes, myocardial necrosis begins. After the myocardial necrosis, symptoms similar to those of a burn appear, such as reddening of the myocardium, blistering, and necrosis. Generally speaking, these symptoms last no less than three days. Many people experience significant improvement after three days because the area of myocardial infarction is relatively small. In patients with extensive myocardial infarction, symptoms can last for 7 days or even longer. During this time, patients may also experience respiratory difficulties, recurrent chest pain, and even sudden death. Therefore, the duration of symptoms in myocardial infarction generally ranges from 3 to 7 days. If there is no improvement within this period, the disease might have led to severe complications.