Sleeping on one’s side and feeling the heart thumping may be physiological phenomenon, congenital heart disease, arrhythmia, etc. 1. Physiological phenomenon: sleeping on the side, especially when lying on the left side, the heart is more close to the chest wall, coupled with the heart is compressed by the body, the heartbeat can be perceived from the chest wall, the sound can disappear after changing the sleeping position. 2. Congenital heart disease: such as atrial septal defect, ventricular septal defect, etc., the heart murmur can be heard at night when you sleep quietly, and you will feel the heart thumping. 3. Arrhythmia: When arrhythmia occurs, patients often have palpitations (rapid heartbeat, often accompanied by panic), i.e., patients can feel their heartbeat, often accompanied by chest tightness, shortness of breath and other discomforts. Side sleep feel heart thumping there are other reasons, should go to the hospital in a timely manner, improve the examination, give targeted treatment after the cause is clear.