A patient with chest pain of recent onset, suggestive for angina pectoris, was referred for diagnostic coronary angiography, which showed the typical phenomenon of "slow dye progression" in the absence of any significant coronary artery stenosis. While intracoronary Doppler measurements confirmed the extremely slow blood flow velocity, the coronary flow reserve and the calculated coronary blood flow proved to be within normal range. The present findings suggest that, in contrast with a previous hypothesis, the phenomenon of slow dye progression may not always be due to a microvascular cause. Epicardial artery disease, as suggested by the marked coronary artery ectasia, may be linked to the slow dye progression and predispose to coronary artery thrombosis.