The coronary flow velocity changes in the great cardiac and middle cardiac veins, induced by intracoronary administration of nitroglycerine, adenosine, and during percutaneous transluminal coronary angioplasty, were evaluated in 12 patients with significant coronary stenoses, using the Doppler wire (Flowire). Optimal spectral signals of the time-averaged peak flow velocity were obtained in 10 patients. Nitroglycerine produced no significant flow velocity changes (P = 0.13). Adenosine caused a significant augmentation of flow velocity compared to baseline (P = 0.003). During balloon inflation, venous flow velocity decreased (P = 0.007); however, the venous outflow did not cease. A pronounced venous hyperemic response, following balloon deflation, was also documented. The utility of continuous vein flow velocity monitoring with the Flowire, during high-risk and complicated coronary interventions remains to be elucidated.