Aims: To determine the effects of digoxin on all-cause mortality and heart failure (HF) hospitalizations, regardless of ejection fraction, accounting for serum digoxin concentration (SDC). Methods and results: This comprehensive post-hoc analysis of the randomized controlled Digitalis Investigation Group trial (n = 7788) focuses on 5548 patients: 1687 with SDC, drawn randomly at 1 month, and 3861 placebo patients, alive at 1 month. Overall, 33% died and 31% had HF hospitalizations during a 40-month median follow-up. Compared with placebo, SDC 0.5-0.9 ng/mL was associated with lower mortality [29 vs. 33% placebo; adjusted hazard ratio (AHR), 0.77; 95% confidence interval (CI), 0.67-0.89], all-cause hospitalizations (64 vs. 67% placebo; AHR, 0.85; 95% CI, 0.78-0.92) and HF hospitalizations (23 vs. 33% placebo; AHR, 0.62; 95% CI, 0.54-0.72). SDC ≥ 1.0 ng/mL was associated with lower HF hospitalizations (29 vs. 33% placebo; AHR, 0.68; 95% CI, 0.59-0.79), without any effect on mortality. SDC 0.5-0.9 reduced mortality in a wide spectrum of HF patients and had no interaction with ejection fraction >45% (P = 0.834) or sex (P = 0.917). Conclusions: Digoxin at SDC 0.5-0.9 ng/mL reduces mortality and hospitalizations in all HF patients, including those with preserved systolic function. At higher SDC, digoxin reduces HF hospitalization but has no effect on mortality or all-cause hospitalizations. © The European Society of Cardiology 2005. All rights reserved.