Background Insulin-like growth factor 1 (IGF-1) promotes favorable cardiac remodeling in heart failure. However, the relation of plasma IGF-1 in patients with various degrees of heart failure is not known. Methods Venous plasma samples were collected from patients with clinically documented heart failure (n = 24) and from control subjects (n = 21) for measurements of IGF-1 levels. In the heart failure group, functional assessment of the physical capacity was determined by means of the New York Heart Association (NYHA) score. Objective determination of ventricular performance was made by transthoracic echocardiographic measurement of left ventricular fractional shortening (FS). Results IGF-1 levels were higher in patients with heart failure (mean age, 67 ± 2 years; 17 men) than in control subjects (age, 71 ± 2 years; 9 men) (20.2 ± 2 mU/L, 14.1 ± 2 mU/L, respectively, P < .05). However, the elevated IGF-1 levels were demonstrated only in patients with mild-to-moderate symptoms (NYHA classes I and II) of heart failure (24.7 ± 3.3 mU/L, n = 12, P = .005 vs control subjects) but not in patients with severe symptoms (NYHA classes III and IV) (15.7 ± 2.3 mU/L, n = 12). There was a strong positive correlation between IGF-1 levels and left ventricular FS (%) (r = 0.58, P = .003, n = 24). Adjustments for other potential confounders including age, sex, treatment received, and underlying cause of heart failure did not alter the relation between IGF-1 and left ventricular FS (odds ratio, 2.01; 95% confidence interval, 1.26 to 6.24; P = .01). Conclusions Plasma levels of IGF-1 show distinct variations with the severity of heart failure and may play a vital role in compensated heart failure. (Am Heart J 2001;142:e10.)