Left ventricular (LV) O2 consumption (V(O2)) per minute is measurable for both regular and arrhythmic beats. LV V(O2) per beat can then be obtained as V(O2) per minute minute divided by heart rate per minute minute for regular beats, but not for arrhythmic beats. We have established that V(O2) of a regular stable beat is predictable by V(O2) = a PVA + b E(max) + c, where PVA is the systolic pressure-volume area as a measure of the total mechanical energy of an individual contraction and E(max) is the end-systolic maximum elastance as an index of ventricular contractility of the contraction. Furthermore, a is the O2 cost of PVA, b is the O2 cost of E(max), and c is the basal metabolic V(O2) per beat. We considered it theoretically reasonable to expect that the same formula could also predict LV V(O2) of individual arrhythmic beats from their respective PVA and E(max) with the same a, b, and c. We therefore applied this formula to the PVA - Emax data of individual arrhythmic beats under electrically induced atrial fibrillation (AF) in six canine in situ hearts. We found that the predicted V(O2) of individual arrhythmic beats highly correlated linearly with either their V(O2) (r = 0.96 +/- 0.01) or E(max) (0.97 +/- 0.03) while both also highly correlated linearly with each other (0.88 +/- 0.04). This suggests that the above formula may be used to predict LV Vo2 of absolute arrhythmic beats from their Emax and PVA under AF.