Effects of laser-heated-tip angioplasty on arteries is not fully understood. We report histology, ultrdsound image properties, and vasoreactivity of human atherosclerotic cornary arteries after exposure to the laser-heated tip catheter. Segments of isolated human coronary arteries were obtained within 5-8 hours postmortem. Side branches were ligated and perfused with Krebs-Ringer solution. Coronary occlusions were recanalized during perfusion using a 1.5-mm tip heated twice with a 10 W argon laser for 10 seconds while two-dimensional 12-MHz ultrasound images were recorded. Images documented vessel recanalization and a n increase in ultrasound refractile properties of vessel walls adjacent and 2-5 mm distal to the heated tip. Histologic studies showed charring along the neolumen and extensive coagulation pattern within the plaque. Vasoreactivity was assessed by measuring flow rate changes during perfusion with 100 ml of lo-'' M serotonin followed by washout with serotonin-free solution. Kecanalized arteries showed a 50% increase in magnitude of vasospasm, which was persistent for 5 hours, compared to control atherosclerotic vessels, which relaxed within 30 minutes. In conclusion, laser-heated-tip-irradiated vessels demonstrated plaque coagulation, increased ultrasound refractile properties of plaque, and increased vasospasm, which persisted for several hours.