Objectives: Suboptimal medication adherence is common among patients with hypertension. Measurements of plasma or urinary levels of antihypertensive drugs are useful, but not widely available. The aim of our study was to investigate the relation of patients' heart rates to their serum beta-blocker levels.Methods: We correlated 220 measurements of serum beta-blocker levels in 106 patients with apparently resistant hypertension to their corresponding office heart rate. A significant proportion, 44.6% of patients, were non-adherent to beta-blocker treatment according to serum level measurement. Non-adherent patients had significantly higher heart rates (80.9 vs. 66.6 bpm, p<.001), systolic (157.4 vs. 147.0mm Hg, p=.002) and diastolic blood pressure (91.1 vs. 87.2mm Hg, p=.041) in comparison to adherent patients.Results: Heart rate above 75.5 beats per minute predicted non-adherence to beta-blocker treatment with a sensitivity of 62.5%, specificity 86.8% and AUC ROC 0.802 (p<.001). Higher heart rate cutoff might be applicable for nebivolol but was not determined due to the low number of patients treated with nebivolol.Conclusions: We concluded that heart rate was shown to be a good predictor of non-adherence to beta-blocker treatment, and might become a quick and easy measure to determine patient adherence in hypertensive patients.