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Figure 1 Study design: patients were studied on two separate occasions: while cardiac resynchronization therapy (CRT) was switched on and after CRT was switched off for 24 h. Serum natriuretic peptides were measured immediately preceding the positron emission tomography (PET) studies. Myocardial blood flow was quantitated using PET and [¹⁵O]water ([¹⁵O]H₂O) at baseline and during adenosine infusion (140 µg/kg/min for 7.5 min). Left ventricular oxidative metabolism was measured using PET and [¹¹C]acetate at baseline and during low-dose dobutamine infusion (5 µg/kg/min for 60 min). Left ventricular function was measured using two-dimensional echocardiography first at rest and then during dobutamine infusion. Open bars = perfusion measurement; solid bars = oxidative metabolism measurement.