- BACKGROUND: Bystander CPR rates remain low. One reason may be that the thought of responding to an emergency is so stressful that it decreases the willingness of laypersons to respond. PURPOSE: The purpose of this study was to quantify the amount of stress experienced by lay responders to a medical emergency and to identify barriers that may have impeded their response to the event. METHODS: Responses from 1243 laypersons responding to an emergency during the Public Access Defibrillation Trial were analyzed in a mixed methods study. Stress related to the event was recorded using a 0 (none) to 5 (severe) scale. Qualitative responses to the question of "What was most difficult?" about the event were analyzed using content analysis. RESULTS: Reported stress levels were low overall (mean 1.2, median 1.0). Laypersons responding to an emergency presumed to be a cardiac arrest had higher stress than those involved in other events (median 2.0 versus 1.0). Stress levels were higher in residential than in public settings (mean 1.41, median 1.0 versus mean 1.13, median 1.0). Those who fit a certain profile (females, non-native English speakers) reported statistically higher stress levels than others. A total of 614 qualitative responses were studied and aggregated into four major categories of difficulty: practical issues; characteristics of the victim; interpersonal issues; thoughts and feelings of the lay responder. Most difficulties were in the category of practical issues. CONCLUSIONS: Among these study volunteer lay responders, low levels of stress were reported. Incorporating descriptions of the difficulties experienced by lay responders in CPR/AED training curricula may make courses more realistic and useful.