Electrocardiogram (ECG) is one of the most commonly performed investigations in emergency departments (EDs), and is an extremely useful adjunct that guides diagnosis, prognosis and treatment. In most cases nurses are the first healthcare professional to assess patients and record an ECG, yet anecdotal evidence suggests that few emergency nurses review, interpret and act on ECG findings. Research suggests this may be due to lack of confidence in, or knowledge about, interpretation of results, often because of inadequate training. This article aims to help emergency nurses understand and interpret the cardiac rhythms commonly encountered on ECGs in EDs, to enable them to support earlier diagnosis and treatment. It describes a simple, five-step method for evaluating the main components of cardiac rhythm.