What to do next?
You are the victim yourself, or you are standing next to the victim, in any case, call 9-1-1 immediately. Assure the person that everything shall be handled quickly and that they are going to be fine. Assurance prior to the arrival of medical aid is quite IMPORTANT since the person going through an attack is on the verge of developing anxiety. Anxiety can be illicit ventricular arrhythmia which deteriorates the condition further.
Moreover, the person can even go into a state of shock due to extreme fear, since they are already in a state of shock. Hence, it is quite necessary that someone should be by the side of the patient to console them until medical aid arrives.