Background: Citizen responder programmes dispatch volunteer citizens to initiate resuscitation in nearby out-of-hospital cardiac arrests (OHCA) before the Emergency Medical Services (EMS) arrival. Little is known about the interaction between citizen responders and EMS personnel during the resuscitation attempt. In the Capital Region of Denmark, emergency physicians are dispatched to all suspected OHCAs. The aim of this study was to evaluate how emergency physicians perceived the collaboration with citizen responders during resuscitation attempts. Method: This cross-sectional study was conducted through an online questionnaire. It included all 65 emergency physicians at Copenhagen EMS between June 9 and December 13, 2019 (catchment area 1.8 million). The questionnaire examined how emergency physicians perceived the interaction with citizen responders at the scene of OHCA (use of citizen responders before and after EMS arrival, citizen responders’ skills in cardiopulmonary resuscitation (CPR), and challenges in this setting). Results: The response rate was 87.7% (57/65). Nearly all emergency physicians (93.0%) had interacted with a citizen responder at least once. Of those 92.5%(n = 49) considered it relevant to activate citizen responders to OHCA resuscitation, and 67.9%(n = 36) reported the collaboration as helpful. When citizen responders arrived before EMS, 75.5%(n = 40) of the physicians continued to use citizen responders to assist with CPR or to carry equipment. Most (84.9%, n = 45) stated that citizen responders had the necessary skills to perform CPR. Challenges in the collaboration were described by 20.7%(n = 11) of the emergency physicians and included citizen responders being mistaken for relatives, time-consuming communication, or crowding problems during resuscitation. Conclusion: Emergency physicians perceived the collaboration with citizen responders as valuable, not only for delivery of CPR, but were also considered an extra helpful resource providing non-CPR related tasks such as directing the EMS to the arrest location, carrying equipment and taking care of relatives.