The slope of preload recruitable stroke work relationship (M_w) is a highly linear, load-insensitive contractile index. To investigate whether M_w can be determined from a single steady-state beat, 45 patients were studied during cardiac catheterization. Single-beat M_w (SBM_w) was calculated directly from the baseline stroke work and left ventricular (LV) end diastolic volume (EDV_B), and the volume axis intercept (V_w) estimated as kxEDV_B+(k-1)xLV_wall, where k is the ratio of the epicardial shell volumes corresponding to V_w and EDV_B and LV_wall is the wall volume. The mean of individual k values was 0.72±0.04, which correlated with the LV mass significantly (r=0.60, p<0.001). SBM_w calculated from a constant k of 0.7 predicted M_w well (r=0.88, p<0.0001), and the prediction improved slightly when k was estimated from individual LV mass (r=0.93, p<0.0001). Subgroup analyses revealed that the single-beat technique also worked in patients with small or large LV mass or volume, or regional wall motion abnormality. Absolute change in SBM_w after dobutamine infusion also correlated with that in M_w. In conclusion, M_w can be estimated from a steady-state beat without alteration of the preload.