The infantile weak physique and exterior defending function make it easy for exogenous pathogenic wind and heat to invade the body through the mouth and nose. The lingering wind and heat accumulated in the lung further attack the meridian of the heart, causing the obstruction of the meridian of the heart and unsmooth circulation of qi and blood. Besides, pathogenic heat scorches nutrient qi and yin, leading to the impairment of both qi and yin of the heart. In both cases mentioned above, palpitation, short breath, chest distress, hypodynamia, etc. can be caused. If the body is weak or both qi and blood are deficient after a severe or febrile disease, the body will be more susceptible to attack by exogenous pathogenic factors, giving rise to the disease.