Context: Vitamin D is associated with decreased cardiovascular-related morbidity and mortality, possibly by modifying cardiac structure and function, yet firm evidence for either remains lacking. Objective: To determine the effects of an active vitamin D compound, paricalcitol, on left ventricular mass over 48 weeks in patients with an estimated glomerular filtration rate of 15 to 60 mL/min/1.73 m 2. Design, Setting, and Participants: Multinational, double-blind, randomized placebo-controlled trial among 227 patients with chronic kidney disease, mild to moderate left ventricular hypertrophy, and preserved left ventricular ejection fraction, conducted in 11 countries from July 2008 through September 2010. Intervention: Participants were randomly assigned to receive oral paricalcitol, 2 μg/d (n=115), or matching placebo (n=112). Main Outcome Measures: Change in left ventricular mass index over 48 weeks by cardiovascular magnetic resonance imaging. Secondary end points included echocardiographic changes in left ventricular diastolic function. Results: Treatment with paricalcitol reduced parathyroid hormone levels within 4 weeks and maintained levels within the normal range throughout the study duration. At 48 weeks, the change in left ventricular mass index did not differ between treatment groups (paricalcitol group, 0.34 g/m 2.7 [95% CI, -0.14 to 0.83 g/m 2.7] vs placebo group, -0.07 g/m 2.7 [95% CI, -0.55 to 0.42 g/m 2.7]). Doppler measures of diastolic function including peak early diastolic lateral mitral annular tissue velocity (paricalcitol group, -0.01 cm/s [95% CI, -0.63 to 0.60 cm/s] vs placebo group, -0.30 cm/s [95% CI, -0.93 to 0.34 cm/s]) also did not differ. Episodes of hypercalcemia were more frequent in the paricalcitol group compared with the placebo group. Conclusion: Forty-eight week therapy with paricalcitol did not alter left ventricular mass index or improve certain measures of diastolic dysfunction in patients with chronic kidney disease. Trial Registration: clinicaltrials.gov Identifier: NCT00497146 ©2012 American Medical Association. All rights reserved.