Heparin – a commonly used anticoagulant – is a high-risk medication and a patient safety risk to both adults and children. This study used a failure mode and effects analysis (FMEA) to prospectively analyze various steps in the preparation, use and disposal of heparin in a pediatric hospital to identify areas of improvement. The FMEA identified 233 potential failures and 737 potential causes of failure. Underlying causes of failure included mathematical errors, EHR challenges, and varying practice and operating procedures (or lack thereof). Countermeasures to address underlying causes are also addressed.