Left ventricular contraction is routinely assessed by radionuclide ventriculography. Although a planar image is conventionally used, tomography has been to improve the detection of wall motion abnormalities. A blood pool image is often used in positron emission tomography on which to superimpose metabolic tracers. Can this image also be used to assess left ventricular contraction? Nine healthy controls, mean (S.D.) age 55 (5) years, and 12 patients, mean (S.D.) age 61 (8) years, with normal, proven or suspected left ventricular damage underwent blood pool tomography with 11CO positron emission tomography (PET) and 99Tcm single photon emission computed tomography (SPECT). A normal value of ejection fraction and range of phase were defined. The normal left ventricular ejection fraction was > or = 37% for PET and > or = 40% for SPECT. The ejection fractions obtained by the two methods in the patient group were positively correlated (r = 0.89, P < 0.001). Abnormalities of left ventricular contraction were detected in nine patients by PET and 10 patients by SPECT imaging. The discrepancy was in a patient with a previous inferior myocardial infarction. Blood pool imaging with 11CO PET can be used to assess left ventricular ejection fraction and regional wall motion.