Coronary blood flow dynamics were investigated in 9 patients with isolated coronary artery disease of the left anterior descending artery (LAD) with good collateral flow (grade 2 or 3 of Rentrop's classification) from the right coronary artery (RCA) and 20 patients with normal coronary arteries as controls. The coronary flow velocity (Vs: systolic peak, Vd: diastolic peak, Vm: mean) was measured with a Doppler catheter and the diameter (D) by the edge detection method in the proximal portion of the RCA. Vs/Vd was calculated. The areas under the velocity curve during systole (integral of s) and diastole (integral of d) were measured to obtain the ratio (integral of s/integral of d). Peak to resting velocity ratio (PRVR) was obtained as an index of coronary flow reserve, using intracoronary injections of 6 ml contrast medium or 8-12 mg papaverine. These parameters before percutaneous transluminal coronary angioplasty (PTCA), after PTCA, and in control subjects were compared. The collaterals disappeared angiographically immediately after successful PTCA. D (before PTCA: 3.2 +/- 0.1 mm, after PTCA: 3.3 +/- 0.1 mm, controls: 3.2 +/- 0.1 mm) and Vs did not vary between before and after PTCA and in control subjects (NS). The values of Vd, Vm decreased and Vs/Vd and integral of s/integral of d increased after PTCA to the values in the controls. PRVR obtained with contrast medium and papaverine also increased.