AbstractDespite expectations that excimer laser ablation would result in a low incidence of coronary dissection, studies have documented a 15–20% incidence of dissection (including a 4–6% incidence of clinically significant dissection) during excimer interventions. This investigation sought to determine if pressure pulses produced by the exposure offluid phasemedia (blood and contrast) to 308‐nm excimer radiation might contribute to unto‐ward outcomes. Pressure pulses generated in these media were quantitated to be>100 atm. In vitro ablation of porcine aorta in the presence of blood or contrast resulted in tissue dissection, while ablation in pure crystalloid did not. Next, a “flush and bathe” technique designed to replace all blood and contrast with crystalloid was applied to a pilot population of 57 consecutive patients. There were no rhythm disturbances or laserrelated clinically significant dissections in this group, and the clinical success rate was 95%. In summary, this report quantitates a potential etiology for excimer dissection and suggests that replacement of blood and contrast with crystalloid might improve procedural and clinical su