The technetium (Tc)-99m pyrophosphate scans have been used to diagnose acute myocardial infarctions and to confirm the equivocal cases. Many articles have been reported about its diagnostic performance and pitfalls. But there has been no evaluation of its predictabillity according to the grades of the radioactivity and statistical evaluation of the trade-off point, i.e., grade 2 and the area under the reciver operating characteristic curve. To achive the hoals. we reviewed 252 cases of -Tc-99m pyrophoshate scans (acute transmural infarction [n=9], acute subendocardial infarction [n=7], unstable angina [n=16], old myocardial infarction [n=19], others [n=111]). The predictabilities of the scan are 98% in grade 4, 84% in grade 3, 83% in grade 2, 53% in grade 1 and 18% in non-uptake. The usual trade-off point, grade 2 is not statistically significant (Z=1.945, p=0.0259>0.01) The area under the receiver operating characteristic curve (Az) is 0.885 Our study shows that the probable main cause of the false negative cases is the time interval between the onset of symptoms and the test.