The literature suggests that pulsatile flow should be routinely used during cardiopulmonary bypass (CPB) in moderate- to high-risk cardiac surgery patients, especially those who must undergo more than 45 minutes of aortic crossclamping. Nevertheless, the use of pulsatile versus nonpulsatile perfusion remains controversial, mainly owing to a lack of precise, complete quantification of pressure-flow waveforms. This editorial briefly summarizes the major factors, or 'basic ABCs, ' that affect the validity of research in this area. A. Because pulsatile flow depends on an energy gradient, investigators must quantify the difference in the hemodynamic energy levels produced by specific pulsatile and nonpulsatile pumps before meaningful direct comparison of these two perfusion modes can be possible. B. The energy equivalent pressure (EEP) formula should be used for this purpose. C. In conducting clinical trials of the perfusion modes, researchers must use appropriate patient-selection criteria, use pulsatile flow continuously during CPB, and choose extracorporeal-circuit components carefully. By following these basic ABCs, researchers will produce more valid and meaningful results that will translate into better outcomes for CPB patients.