Introduction: Over-ventilation can compromise coronary perfusion pressures during cardiopulmonary resuscitation (CPR) and should be minimised. We compared ventilations during manual and mechanical (load-distributing band -LDB) CPR, which gives ventilation prompts. Our primary objective was to compare the ventilation rate between manual CPR and LDB-CPR. Method: This was a phased, non-randomised study at a tertiary hospital emergency department. All out-of-hospital, non-traumatic cardiac arrest adult patients during the study period from February 2007 till July 2008 were eligible. Pregnant females and patients aged less than 18 years of age were excluded. Ventilation rates in the first and second 5 minutes segments were recorded. Over-ventilation was defined as ventilation rate above 12 breaths per minute. All data analyses were performed with SPSS, version 17.0. Mean differences with 95% confidence interval (CI) were compared between the 2 treatment groups. Results: From February 2007 till August 2007, there were 29 patients with manual CPR; and from September 2007 till July 2008, there were 62 with LDB-CPR. In the first 5 minutes of CPR, the proportion of patients that were over-ventilated, was 27.6% (manual) and 4.8% (LDB) (difference = 22.7%; 95% CI: 3.5-46.4%). In the next 5 minutes, the proportion of patients that were over-ventilated was 37.9% and 1.6% for manual and mechanical CPR respectively (difference = 36.3%; 95% CI: 16.5-58.9%). Conclusion: Over-ventilation is reduced significantly in LDB-CPR compared to manual CPR during the first and second 5 minutes of resuscitation.