People exposed to a violent event such as a terrorist attack present various reactions to stress that may need an emergency intervention and first some specific traumatic stress evaluation. The latter is crucial when it comes to determine those who will develop severe and disabling troubles likely to last several years. It is demonstrated that theses troubles are particularly severe when they are related to human designed traumatic events as terrorism. 5 to 20% will develop psychiatric post-traumatic symptoms. Of all those concerned, health care professionals have to determine those for whom a severe evolution is dreaded. It is crucial to make their taking care of a priority. We will indicate the best predictive factors of a pathological evolution hereafter. We will present the most useful questionnaires and clinical characteristics to identify subjects with the higher risk of PTSD. According to these criteria a health care strategy is going to be determined. Identifying the predictive factors concerns the individual peritraumatic reactions as well as the traumatic event itself. Thus it is necessary to take into account the previous health state of the person and the early help provided. Among the initial reaction characteristics several clinical studies suggest that measuring the heart beat is an indicator to emotional reaction. A heart beat superior to 92 per minute could predict a PTSD to come. This simple physiological indicator added to more specific psychological and peritraumatic dissociation ones could be the best actual PTSD predictive factors.