- There is controversy regarding type of bundle branch block (BBB) that is associated with increased mortality risk in patients with heart failure (HF). The present study was designed to explore the association between BBB pattern and long-term mortality in hospitalized patients with systolic HF. Risk of 4-year all-cause mortality was assessed in 1,888 hospitalized patients with systolic HF (left ventricular ejection function <50%) without a pacemaker in a prospective national survey. Cox proportional hazards regression modeling was used to compare mortality risk in patients with right BBB (RBBB; 10%), left BBB (LBBB; 14%), and no BBB (76%) on admission electrocardiogram. At 4 years of follow up, mortality rates were highest in patients with RBBB (69%), intermediate in those with LBBB (63%), and lowest in those without BBB (50%, p <0.001). Multivariate analysis demonstrated a significant 36% increased mortality risk in patients with RBBB versus no BBB (p = 0.002) but no significant difference in mortality risk for patients with LBBB versus no BBB (hazard ratio 1.04, p = 0.66). RBBB versus LBBB was associated with a 29% (p = 0.035) increased risk for 4-year mortality in the total population and with a 58% (p = 0.015) increased risk in patients with ejection fraction <30%. In conclusion, RBBB but not LBBB on admission electrocardiogram is associated with a significant increased long-term mortality risk in hospitalized patients with systolic HF. Deleterious effects of RBBB compared to LBBB appear to be more pronounced in patients with more advanced left ventricular dysfunction.