The purpose of the current study was to clarify the myocardial kinetics of technetium-99m sestamibi when the latter is administered during reperfusion. Sestamibi has in the past been given to patients following thrombolytic therapy to document reperfusion and assess salvage. However, the factors which affect sestamibi kinetics during reperfusion are not clearly defined. In this study the left circumflex coronary artery was occluded for 2 h in six dogs (group 1) and for 3 h in six dogs (group 2), followed by reperfusion. Five additional dogs were not reperfused (group 3). Sestamibi was administered during reperfusion in groups 1 and 2, and during ongoing occlusion in group 3. Regional myocardial sestamibi activity was monitored for 3 h using miniature implanted radiation detectors and gamma camera imaging. Group 1 dogs had no infarcts, group 2 had moderate infarcts (mean: 13.9%), and group 3 had large infarcts (mean: 25.2%). Three-hour fractional myocardial clearances were significantly greater for reperfused infarcted (group 2) (0.23 +/- 0.02 SEM) and for nonreperfused infarcted myocardium (group 3) (0.24 +/- 0.02) compared to control (0.10 +/- 0.01) and reperfused noninfarcted myocardium (group 1) (0.07 +/- 0.02; P < 0.01). Quantitative image analysis demonstrated a significant reduction in the left circumflex/left anterior descending count ratios from initial to final scans for group 2 (0.74 +/- 0.03 to 0.65 +/- 0.03, P < 0.05), and a trend towards a reduction in the count ratios from initial to final scans for group 3 (0.38 +/- 0.04 to 0.30 +/- 0.04; P = 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)