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Figure 5 Data from a Group 3 dog with non-critical left anterior descending and left circumflex artery stenoses at peak dobutamine dose when myocardial blood flow is increased. Perfusion defects (PDs) (arrows) (A) early (1 s) and (C) late (5 s) after microbubble destruction showing little filling-in because of reduced collateral blood flow. Both are similar in topology to the hypoperfused zones by radiolabeld microsphere (B). (D) End-systolic image with extent of abnormal wall thickening (defined by chords and arrows) in the latter, corresponding to the PDs. This region also includes the better perfused myocardium between the two PDs seen in (A) and (C).