This study sought to determine whether using the Resuscitation Council UK’s iResus© application on a smart phone improves the performance of doctors trained in advanced life support in a simulated emergency. Thirty-one doctors (advanced life support-trained within the previous 48 months) were recruited. All received identical training using the smart phone and the iResus application. The participants were randomly assigned to a control group (no smart phone) and a test group (access to iResus on smart phone). Both groups were tested using a validated extended cardiac arrest simulation test (CASTest) scoring system. The primary outcome measure was the overall cardiac arrest simulation test score; these were significantly higher in the smart phone group (median (IQR [range]) 84.5 (75.5–92.5 [64–96])) compared with the control group (72 (62–87 [52–95]); p = 0.02). Use of the iResus application significantly improves the performance of an advanced life support-certified doctor during a simulated medical emergency. Further studies are needed to determine if iResus can improve care in the clinical setting.