To evaluate coronary flow dynamics after direct angioplasty and to define the determinants of flow-velocity variables in the infarct artery, we measured coronary flow velocity in 36 infarct arteries and 64 normal coronary arteries by using a Doppler guide wire. Flow-velocity variables in the infarct arteries did not return to normal even after successful direct angioplasty, and phasic coronary flow in infarct arteries varied considerably. Normal phasic flow was calculated as the ratio of diastolic to systolic flow ratio (DSVR) of greater than or equal to mean DSVR - 1 SD in normal coronary arteries. Infarct-related arteries were divided into two groups: normal DSVR (n = 28) and low DSVR (n = 8). Reduced diastolic peak velocity with a relative preservation of systolic velocity contributed to a low DSVR flow. Angiographic slow flow and late recanalization were significantly related to low DSVR flow. Thus the extent of disturbed microcirculation can be evaluated by assessing phasic flow after direct angioplasty for acute infarction.