Background: ⁸²Rb PET and [¹⁵O]H₂O PET are both validated tracers for myocardical perfusion imaging but have not previously been compared clinically. During our site’s transition from ⁸²Rb to [¹⁵O]H₂O PET, we performed a head-to-head comparison in a mixed population with suspected ischemic heart disease. Methods: A total of 37 patients referred for perfusion imaging due to suspicion of coronary stenosis were examined with both ⁸²Rb and [¹⁵O]H₂O PET on the same day in rest and during adenosine-induced stress. The exams were rated by two blinded readers as normal, regional ischemia, globally reduced myocardial perfusion, or myocardial scarring. For [¹⁵O]H₂O PET, regional ischemia was defined as two neighboring segments with average stress perfusion ≤ 2.3 mL/(min·g). Further, we evaluated a total perfusion deficit (TPD) of ≥ 10% as a more conservative marker of ischemia. Results: [¹⁵O]H₂O PET identified more patients with regional ischemia: 17(46%) vs 9(24%), agreement: 59% corresponding to a Cohen’s kappa of.31 [95%CI.08-.53], (P < .001). Using the more conservative TPD ≥ 10%, the agreement increased to 86% corresponding to a kappa of.62 [95%CI.33-.92], (P = .001). For the subgroup of patients with no known heart disease (n = 18), the agreement was 94%. Interrater agreement was 95% corresponding to a kappa of.89 [95%CI.74-1.00] (P < .001). Conclusions: In clinical transition from ⁸²Rb to [¹⁵O]H₂O PET, it is important to take into account the higher frequency of patients with regional ischemia detected by [¹⁵O]H₂O PET. Graphical Abstract: [Figure not available: see fulltext.].