Increased heart rate in babies with fever is caused by an increase in body temperature and is normal. Because the body’s fluid regulation is impaired when the body temperature rises, it is not able to regulate the heart rate and respiration normally, and the metabolism is accelerated, so when the fever is accompanied by an increase in heart rate and respiration. The higher the body temperature, the faster the heart rate and the faster the respiration, and the body temperature is directly proportional to the heart rate and respiration. When a baby has a fever, the metabolism in the body is accelerated, and the heart and lung function will become hypoxic, so there will be an increase in heart rate and respiration. This increase in heart rate is physiological, and the heart rate and breathing can return to normal after the body temperature returns to normal. The younger the baby, the greater the chance of fever, because the younger the baby, the faster the basic metabolism, the body temperature regulation center is not well developed, the higher the chance of fever.