Regression of left ventricular hypertrophy (LVH) is feasible with more frequent hemodialysis (HD). We aimed to ascertain pathways associated with regression of left ventricular mass (LVM) in patients enrolled in the Frequent HD Network (FHN) trials. This was a post hoc observational cohort study. We hypothesized LVH regression with frequent HD was associated with a different cardiovascular biomarker profile. Regressors were defined as patients who achieved a reduction of more than 10% in LVM at 12 months. Progressors were defined as patients who had a minimum of 10% increase in LVM at 12 months. Among 332 randomized patients, 243 had biomarker data available. Of these, 121 patients did not progress or regress, 77 were regressors, and 45 were progressors. Mean LVM change differed between regressors and progressors by -65.6 (-74.0 to -57.2) g, p < 0.001. Regressors had a median (interquartile range) increase in dialysis frequency (from 3.0 [3.0-3.0] to 4.9 [3-5.7] per week, p = 0.001) and reductions in pre-dialysis systolic (from 149.0 [136.0-162.0] to 136.0 [123.0-152.0] mm Hg, p < 0.001) and diastolic (from 83.0 [71.0-91.0] to 76.0 [68.0-84.0] mm Hg, p < 0.001) blood pressures. Klotho levels increased in regressors versus progressors (76.9 [10.5-143.3] pg/mL, p = 0.024). Tissue inhibitors of metalloproteinase (TIMP)-2 levels fell in regressors compared to progressors (-7,853 [-14,653 to -1,052] pg/mL, p = 0.024). TIMP-1 and log (brain natriuretic -peptide [BNP]) levels also tended to fall in regressors. Changes in LVM correlated inversely with changes in klotho (r = -0.24, p = 0.014). -Conclusions: Markers of collagen turnover and changes in klotho levels are potential novel pathways associated with regression of LVH in the dialysis population, which will require further prospective validation.