Background: Performing cardiopulmonary bypass is a complex task which involves evaluating visual input from patient monitors and technical parameters displayed at the heart-lung machine console as well as reacting to other sensory input. Only few studies are available concerning the competency requirements for clinical cardiovascular perfusionists, including attention, perception, and coping with mental stress. This study aims at evaluating attention, perception, and stress levels of clinical cardiovascular perfusionists during cardiopulmonary bypass. Methods: Nine clinical cardiovascular perfusionists voluntarily offered to participate in the study. Participants were asked to wear Tobii 2 eye-tracking glasses throughout the procedures. Specific time points were analyzed (cardiopulmonary bypass on, initial cardioplegia delivery, steady state, cross-clamp off, and weaning from cardiopulmonary bypass). Data acquisition was supplemented by participants’ self-evaluation regarding their stress levels and by National Aeronautics and Space Administration Task Load Index (NASA TLX) questionnaires. Results: Seven datasets were sufficient to be evaluated. The clinical cardiovascular perfusionists’ professional experience ranged from 0.5 to 24 years. Evaluation of eye-tracking data revealed large variations in areas of interest hits, fixation, and dwell times. Across all phases, the venous reservoir, mean arterial pressure, arterial pump display, cardioplegia control, and data management system received the highest levels of attention. Pupil diameter measurements increased at start of cardiopulmonary bypass, cardioplegia delivery, and weaning off, but returned to base level during steady state. Clinical cardiovascular perfusionists’ self-evaluation showed that subjective stress level was highest at the start and the end of the procedure. NASA TLX questionnaires revealed medium-to-high mental and temporal workloads, but low physical workloads. Performance, effort, and frustration indices showed medium workloads. Conclusion: During cardiopulmonary bypass, perfusionists are subjected to stress. Peak stress levels were highest during start and end of cardiopulmonary bypass. Furthermore, visual attention and perception varied between the operative phases. Further studies are indicated to evaluate the design of heart-lung machines and stress-coping strategies during cardiopulmonary bypass.