A lie down heart beat hard may be related to the daytime activity is greater, the increase in the amount of blood back to the heart and other factors. 1. Daytime activity is relatively large: the energy or attention is scattered, the attention to the body is relatively low, lying down quietly after the attention to their own bodies increased, so will feel the heartbeat or feel the heartbeat fast. 2. Increase in the volume of return blood: when lying down, the volume of return blood increases, the heart load increases, the heart muscle needs to increase the contraction force or heartbeat frequency to beat out the increase in return blood, so it may cause the heart to beat faster or even accompanied by palpitations. A lying down heartbeat is strong if the feeling is very obvious, it is best to go to the hospital to do the relevant examination, such as 24-hour dynamic electrocardiography, cardiac ultrasound, and so on. Under the guidance of the doctor to identify the cause and then actively treat.