The slope of the 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 baseline left ventricular (LV) end-diastolic volume (EDV_B), and the volume-axis intercept (V_w) was estimated as k × EDV_B + (k  1) × LV_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 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 with regional wall motion abnormalities. The 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 preload.