Comprehensions of how technology-mediated environments work are marked by a lack of theoretical sophistication about how expertise emerges and develops. Using a practice-based approach to workplace learning and knowing, a case of telecardiological consultation is discussed, where a dedicated call center works by connecting general practitioners (GPs)with remote cardiologists. The service allows GPsto send electrocardiogram traces (ECGs) and discuss the needs of patients with a cardiologist. The role of materials (ECG traces, the recording machine, infrastructure), and communication (synchronous communication in the form of a phone call) are considered in the practical application of the service. It isargued that being an expert telecardiologist entails the ability to align heterogeneous elements, and co-construct, a reliableinterpretation of the patient’s situation alongside a doctor. To do that when the situation is not immediately clear, necessitates both doctors discursively mobilize different bio-physiological, chemical, material, social and psychological aspects of a patient’s condition, in order to arrive at a reliable interpretation. Thanks to a practice-based sensitivity, Ianalyze the case study reading these interactions as competent material-discursive practices.