Cardiac R2* changes were logarithmically proportional to final LIC. r = 0.70; P < .001. Drug efficacy appears to increase sharply as LIC approaches the normal range; all patients with final LIC less than 5 mg improved their cardiac iron. Solid line represents a linear fit to log-transformed LIC values. The white region represents significant cardiac iron clearance; light gray region, no statistically significant individual change; and dark gray region, significant cardiac iron accumulation.