Copeptin is cosynthesized with vasopressin, also known as antidiuretic hormone, with plasma levels similar to vasopressin. In the past 2 years, copeptin has been studied as a diagnostic and prognostic marker in infections and other diseases. In patients with destabilized heart failure, copeptin is an accurate prognostic marker for mortality. The aim of this study was to assess copeptin in orthotopic heart recipients in relation to New York Heart Association class and kidney function. The studies were performed on 139 prevalent patients after orthotopic heart transplantation-(OHT) including 105 males and 34 females. Glomerular filtration rate (GFR) was estimated using simplified Modification of Diet in Renal Disease (MDRD), Cockcroft-Gault, and new the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation. In addition 24-hour creatinine clearances were performed on each patient. Complete blood count, urea, serum lipids, fasting glucose, creatinine, BNP were studied by standard laboratory method in the hospital central laboratory. Plasma copeptin was measured using a commercially available kit. Copeptin correlated with parameters of kidney function: creatinine (r = .39, P < .001), estimated GFR by MDRD (r = -.24, P < .01), estimated GFR by CKD-EPI (r = -.25, P < .01), creatinine clearance by Cockcroft-Gault (r = -.27, P < .01), 24-hour creatinine clearance (r = -.21, P < .05), cystatin C (r = .45, P < .001), and high-density lipoprotein (r = .18, P < .05), BNP (r = .25, P < .01), intraventricular septal diameter/thickness (IVS); r = -.30, P < .01), ejection fraction (r = -.17, P < .05), ferritin (r = .21, P < .05). Upon multiple regression analysis, predictors of copeptin were cystatin C and IVS, which explained 51% of copeptin variations (F = 3.21, P < .03 and Standard error of estimate was 0.57). Beta value for cystatin C was 0.51 (P = .024) and for IVS was -0.59 (P = .018). Copeptin in a heart transplant population was independently associated with kidney function and IVS.