Aim. Blood pressure (BP) determination in atrial fibrillation (AF) patients remains challenging due to its high inter-measurement variability. The novel methodology of precise beat-to-beat BP determination may be used to guide the hypotensive therapy selection and adjustment, but along with that provides additional opportunity for the investigation of hemodynamics in patients with chronic AF. Material and method. The study sample consisted of 60 patients with the main diagnosis of grade II-III arterial hypertension; 30 of those were on sinus rhythm and 30 had chronic non-valvular AF. In all patients HR was within the limits recommended for left ventricular ejection fraction of >40%. Beat-to-beat systolic, diastolic, and pulse BP (SBP, DBP, and PBP, respectively) assessment at each heart beat within 15 minute interval was performed with “Kardiotekhnika-SAKR” system (NAO “Incart”, St.Petersburg, Russia). Results. Mild RR-interval variations, observed on sinus rhythm, resulted in insignificant SBP, DBP, and PBP fluctuations. More prominent RR-interval irregularity, typical for AF, is accompanied by more significant SBP, DBP, and PBP deviations. As mean SBP of each patient was taken for 1,0, “normal” SBP (≥0,9) was seen in RR-intervals of 754±58 msec; “markedly decreased” (<0,9)-in 619±66 msec; “prominently decreased” (<0,8)-in 527±86 msec; “severely decreased” (<0,7)-in 489±38 msec. For DBP (mean DBP of each patient was taken for 1,0) “normal” DBP (<1,1) was seen in RR-intervals of 758±63 msec; “markedly increased” (>1,15)-in 587±38 msec; “prominently increased” (>1,2)-in 566±38 msec; “severely increased” (>1,2)-in 539±41 msec. For PBP (mean PBP of each patient was taken for 1,0) “normal” PBP (≥0,75) was seen in RR-intervals of 770±58 msec; “markedly decreased” (<0,75)-in 561±40 msec; “prominently decreased” (<0,5)-in 520±33 msec; “severely decreased” (<0,25)-in 510±52 msec. Proportion of heart beats with insufficient efficacy according to PBP level (sum of “markedly”, “prominently”, and “severely” decreased) was 16,4±5,1% with prominent individual deviations (5,9-25,7%). Mean range of RR-interval providing to “marked” PBP decrease was 147±26 msec, also with significant individual variations-55-235 msec. Conclusions. Beat to beat BP measurement is characterized by high level of accuracy. In addition to mean SBP and DBP, their beat-to-beat fluctuations can be determined, which might be significant in irregular rhythm. This might help in selection of individualized anti-hypertensive therapy. The study has shown that along with RR-intervals shortening the number of hemodynamically insufficient heart beats increased, which manifested by SBP decrease, DBP increase, resulting in decrease of PBP. However, this general consistent pattern masks the individual differences of heart rhythm structure in AF. This method can help to determine the optimal HR for each individual patient with AF.