The objective of this study is to develop a reliable Tablet-PC based observational tool for identifying work systems factors that impact cardiac surgical care. Using the tool we observed 26 open heart surgeries over a five-month period. In thirteen of the 26 observations, both observers stood in the same location and in the other thirteen cases the observers stood in different locations within the operation room (OR). The surgical cases typically last five hours and were conducted in multiple operating rooms within the hospital and with mixed surgical teams. There was an average of 8.49 flow disruptions per hour related to work system factors with an average of 42.45 disruptions per case. Results revealed that inter-rater reliability in identifying work system factors that disrupted surgical flow was roughly 87% when observers were standing in the same location. However, when standing in different locations, the reliability decreased to an average of 75%.