The duration of the cardiac injection varies depending on the method of injection. If it is injected subcutaneously, the effect usually appears in 3-5 minutes and can be maintained for about 1 hour; if it is injected intramuscularly, its effect can be maintained for about 30 minutes. Cardiac injection is a positive inotropic drug, including two types of epinephrine and norepinephrine, and is mostly used for emergency treatment of patients in cardiac arrest, shock and bronchial asthma. Its effect is to increase the excitability of the heart, increase the contraction force of the heart muscle, increase the conduction speed, accelerate the heart rate, contract the mucous membrane, skin and visceral blood vessels, raise the blood pressure and keep the blood pressure at a normal level; it can also dilate the coronary arteries and improve the blood supply to the heart; relax the smooth muscle of the gastrointestinal tract and bronchus and release the bronchial spasm; it can also promote the decomposition of glycogen and make the blood sugar rise for the body’s energy supply. However, these drugs are prone to side effects. If the drug is used for too long or in too large a dose, it can cause cardiac arrhythmia, and drug leakage can also cause local tissue necrosis.