The authors studied the changes in coronary blood flow before, during and after reperfusion by angioplasty of the disease coronary vessel responsible for myocardial infarction using intracoronary Doppler. Forty patients aged 60.2 +/- 15.4 years, admitted for primary myocardial infarction (inferior: 22, anterior: 18) were included. Before reperfusion, the peak velocity of the collateral coronary circulation was 14.8 +/- 8.1 cm/s. The flow was bidirectional, mainly retrograde (N = 32), negative (N = 1) or positive (N = 5). The five Rentrop 0 patients had velocities similar to Rentrop 1, 2 or 3 patients (Rentrop 0: 14.9 +/- 6.4 cm/s; Rentrop 1: 12.3 +/- 9.9 cm/s; Rentrop 2: 15.2 +/- 8.2 cm/s; Rentrop 3: 17.5 +/- 6.3 cm/s). Patients with TIMI 3 reperfusion flow had the highest APV Doppler velocities (average peak velocities during the cardiac cycle) (APV TIMI 3 = 20.2 cm/s versus APV TIMI 1 and 2 = 10.9 cm/s, p = 0.05). After angioplasty, the APV was 18.7 +/- 10.4 cm/s (p < 0.001). Diastolic flow was dominant. Seventeen patients had retrograde systolic flow, 12 had minimal systolic flow and 17 had a steep diastolic deceleration slope. Intracoronary Doppler demonstrates the wide range of coronary flow in TIMI 3 flow patients, both from the morphological and the quantitative points of view, which seems to be independent of the presence of residual stenosis and could be related to abnormalities of the microcirculation. This could allow identification of a subgroup of patients at high risk and candidates for a complementary therapeutic intervention (intra-aortic balloon pumping...).