The relation between hematocrit and progression from asymptomatic left ventricular (LV) systolic dysfunction to symptomatic heart failure (HF) was examined in 2,821 patients from the Studies of Left Ventricular Dysfunction Prevention trial. Patients in the lowest hematocrit quartile (hematocrit < or = 40%) were at increased risk for the development of HF symptoms (hazard ratio [HR] 1.79, 95% confidence interval [CI] 1.37 to 2.34), first HF hospitalization (HR 2.35, 95% CI 1.52 to 3.62), and death or the development of HF symptoms (HR 1.60, 95% CI 1.28 to 1.99) compared with patients in the highest hematocrit quartile (hematocrit > 46%).