The myocardial uptake of technetium-99m pyrophosphate (99mTc-PYP) in perimyocarditis induced by coxsackievirus B3 in BALB/c mice was studied. 9"mTc-PYP uptake ratio, measured by the ratio of counts/min per gram for the heart to counts/min per gram for the skull, began to increase 5 days after virus inoculation when myocardial necrosis was evident. On the seventh day after the inoculation, 9ImTc-PYP ratio reached a maximum. Histologically, fine, dystrophic calcification appeared in the necrotic

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... ibers. 99mTc-PYP uptake was in proportion to the extent of the myocardial lesions. Thereafter, cellular infiltrations increased with time and were most severe on the fourteenth day, but 9gmTc-PYP ratio had begun to fade. On the twentyeighth day, perimyocardial fibrosis increased and calcification was still present, but 9ImTc-PYP ratio had decreased. Myocardial uptake with severe pathologic lesions was visualized on a whole-body image on the seventh day after inoculation with the virus. The findings may provide a basis upon which 99mTc-PYP imaging may be applied to viral perimyocarditis in humans.