BACKGROUND:Limited data are available in our region on out-of-hospital treatment of cardiac arrest. The aim of this study is to evaluate whether the changes implemented in the emergency system (i.e. an increased number of basic life support and advance life support crews that were dispatched) produced the expected outcome improvements. METHODS:(a) EXPERIMENTAL DESIGN:data were prospectively collected on patients with sudden out-of-hospital cardiac arrest in three emergency dispatch centers for 3 months during two study periods, year 2000 and year 2003, differentiated only by the increase of qualified crews. Outcomes and survival were evaluated at 24 h and 1 month after the event. (b) SETTING:out-of-hospital treatment. (c) PATIENTS:352 (174 in the second study period) patients suffering cardiac arrest. (d) INTERVENTIONS:the study was observational. RESULTS:We could document, between the two study periods, stable 24 h (12.6 vs 9.1%) and 1 month survival (3.4 vs 5.8%, NS). Nevertheless, arrival time on site was significantly higher in the second period (from 8.3+/-3.3 to 10.1+/-5.4 min, P<0.05). CONCLUSIONS:The strengthening of only one link of the chain-of-survival did not improve 1 month survival.