Fifteen patients with clinical and electrocardiographic features of acute pericarditis underwent myocardial scintigraphy using 99mTc-pyrophosphate. All had normal images. In 5 additional patients with acute pericarditis and evidence of ischemic heart disease, 99mTc-pyrophosphate images showed focal abnormalities in 2 patients and equivocal findings in 2. Serial myocardial radionuclide images were obtained 2 to 18 days after induction of pericarditis in 8 dogs; all images were normal. No stainable tissue calcium was demonstrated histochemically in the pericardium or myocardium of these dogs. The results suggest that 99mTc-PYP myocardial radionuclide images are normal in acute pericarditis in the absence of ischemic heart disease.