Purpose <p>To determine the most important patient factors influencing quantitative MBF and to report the lower (LRL) and upper (URL) reference limits for 13N-ammonia positron emission tomography (PET) myocardial perfusion imaging (MPI).</p> Methods <p>Patients who underwent 13N-ammonia PET-MPI were screened, and those with evidence of myocardial ischemia or scar, known cardiomyopathy, impaired left ventricular function, non-response to vasodilators, and those who underwent a stress-rest protocol were excluded. Multiple linear regression analyses were performed to identify independent predictors of rest MBF (rMBF), stress MBF (sMBF), and myocardial flow reserve (MFR), and predictor importance was calculated. Finally, median, LRL, and URL for rMBF, sMBF, and MFR were calculated based on the presence of predictors.</p> Results <p>Among 784 patients with a median coronary artery calcium score (CACS) of 69, median rMBF was 0.75mL∙min^− 1∙g^− 1 (LRL = 0.49 mL∙min^− 1∙g^− 1; URL = 1.33 mL∙min^− 1∙g^− 1), median sMBF was 2.41mL∙min^− 1∙g^− 1 (LRL = 1.42 mL∙min^− 1∙g^− 1; URL = 3.73 mL∙min^− 1∙g^− 1), and median MFR was 3.09 (LRL = 2.11; URL = 4.65). The body mass index (BMI) was the single most important independent predictor of rMBF, sMBF, and MFR (predictor importance of 72%, 87%, and 41%, respectively; standardized β=-0.434, -0.566 and − 0.174, respectively). Additional predictors were sex and hypertension for rMBF, sex for sMBF, and hypertension and CACS for MFR.</p> Conclusion <p>In patients without flow-limiting CAD, MBF is strongly influenced by the patient’s habitus, whereby median and reference limits for sMBF and rMBF decrease with increasing BMI. Consequently, MFR exhibits stable lower reference limits across a wide range of BMI and may be considered the most robust quantitative parameter derived from 13N-ammonia PET-MPI.</p>