The diagnostic accuracy of ECG gated blood pool SPECT (blood pool SPECT) for detecting and quantify postinfarction left ventricular aneurysm (LVA) was assessed in 49 patients with myocardial infarction and 15 control subjects. LVA, which was detected in 35 of 49 patients, was defined as a regional protrusion through a cardiac cycle in contrast ventriculography and as a non-contracting segment with a markedly delayed phase angle in the tomographic functional images derived from phase analysis. The blood pool SPECT technique showed a high sensitivity (100%), specificity (78.6%) and accuracy (93.3%) for detecting LVA and was very useful for precisely determining LVA location and sizing contractile and non-contractile volume of left ventricle in patients with LVA. Furthermore, left ventricular ejection fraction (LVEF) after the excision of LVA was predicted using preoperative pool SPECT images in 9 patients. The predicted LVEF was closely correlated with the measured LVEF after the operation (y = 1.09x-4.37, r = 0.87, p less than 0.01). Thus, gated blood pool SPECT can be a useful non-invasive technique not only for detecting and quantifying left ventricular aneurysm but also for predicting a residual left ventricular function after aneurysmectomy.