High counting statistics with 99mTc-sestamibi make gated SPECT imaging realistic. Information obtained with gated and nongated SPECT were compared in 83 subjects (20 normals, 63 patients) using a 1-day protocol (250 MBq [6 mCi] rest, 900 MBq [24 mCi] peak stress). Studies were acquired for eight frames/RR interval and formatted to a standard nongated study, a study consisting of diastolic (DIA) frames and dynamic functional studies. The right ventricle appeared more distinct in DIA than in nongated studies (p < 0.01). The left ventricular cavity was larger in DIA studies (p < 0.001), leading to more coronal slices with cavity (p < 0.001). A strong inverse relation between left ventricular cavity size in nongated studies and increase in cavity size and in number of coronal slices with cavity in DIA studies was found (r = -0.74 and -0.67, both p < 0.001). Severity (extent and degree) of perfusion abnormalities in rest and stress studies, assessed quantitatively in 50 patients (20 normals as reference), correlated highly in nongated and DIA studies (r = 0.98, p < 0.001). Severity of small and moderate sized perfusion defects showed a high degree of agreement in nongated and DIA studies, while severity of large defects was less pronounced in DIA studies (p < 0.05). In patients with subtle perfusion abnormalities, the results from DIA imaging agreed best with clinical data.