Understanding physician cognitive workflow while using Electronic Health Records (EHRs) and how the user interface interaction can support cognitive workflow is essential to premium patient care. One way to further understand the relationship between physician cognitive workflow and the user interface is through usability evaluations. The purpose of this paper is to present, test and analyze a usability evaluation method that is robust and yet flexible enough to understand the complexity and needs of a physicians' cognitive workflow when using an EHR system. Further, our usability evaluation method was designed from the perspective of the physician, rather than an information technology perspective. Important contributions of this study are that we demonstrate a way to evaluate an EHR in the actual cardiac care setting and produce results that identify actionable and realistic system improvement recommendations.