The measurement of regional myocardial blood flow (MBF) with (H2O)-O-15 and PET requires an additional (CO)-O-15 blood-pool scan for the purpose of region of interest (ROI) definition. This additional scan results in a substantially increased radiation dose, study duration and risk of movement artifacts. Therefore, a method was developed to generate myocardial factor images directly from the dynamic (H2O)-O-15 study without the need for a (CO)-O-15 scan. Methods: The factor sinograms were generated by means of linear dimension reduction of the dynamic sinograms, where the required variate and covariate factors (myocardial and blood time-activity curves) were modeled from the lung time-activity curve. The factor images were generated by iterative reconstruction. Results: No significant difference was found between MBF values from ROls drawn on the traditional images (using the (CO)-O-15 scan) and those drawn on the factor images. Conclusion: It is possible to generate myocardial images directly from the dynamic (H2O)-O-15 study, so that the (CO)-O-15 scan can be omitted from MBF studies. The proposed method is robust and results in nearly optimal signal-to-noise ratios in the factor images.