Critical ultrasound presents explosive growth in recent years, which can be used in procedure assistance, diagnosis clarification, treatment guidance, and cardiopulmonary resuscitation.First of all, critical ultrasound can be performed to determine the cardiac arrest or not.Secondly, it can be used to help differentiate the type of cardiac arrest, especially the ventricular fibrillation and asystole.Finally but maybe the most importantly, critical ultrasound can be used to discern the pseudo pulseless electrical activity (PEA), identify the cause to avoid the true cardiac arrest with the treatment and cure measures to the point.Focused echocardiography evaluation in life support (FEEL) can be conducted in cardiopulmonary resuscitation (CPR) process without interrupt to an extreme, which integrated the critical ultrasound and CPR, and was recommended by the 2015 American Heart Association Guidelines Update for cardiopulmonary resuscitation and emergency cardiovascular care.