Introduction: Voltage-gated K (Kv) channels control resting membrane potential and action potential repolarization in excitable cells of the cardiovascular system. Ancillary Kvβ subunits bind NAD(P)(H), thereby linking cellular metabolism and membrane excitability. Elevated myocardial O2 consumption, (e.g., during exercise), promotes enhanced blood flow and modulates cardiomyocyte repolarization in a Kvβ2-dependent manner.Hypothesis: Adaptive cardiac growth during chronic exercise training requires Kvβ2.Methods: We subjected wild type (wt; S129) and age-matched Kvβ2 mice to an established protocol of low intensity forced treadmill running (FTR) for 4 weeks. To evaluate exercise capacity, we performed tests consisting of progressive increases in speed and incline angle to determine total work performed (kg·m) prior to exhaustion. To assess myocardial adaptation to exercise, we compared heart mass, cardiomyocyte cross sectional area, and biochemical markers of hypertrophy (i.e., CEBP/β, Cited4, nfatc2) between FTR and sedentary (sed) control animals.Results: Total work (pre- and post-FTR) and FTR compliance (i.e., completed sessions and total exercise time) were similar between wt- and Kvβ2-FTR groups. Wild type-FTR mice exhibited significantly greater heart mass, normalized to tibia length, compared with wt-sed animals (wt-FTR: 6.4 ± 0.2; wt-sed: 5.3 ± 0.3; P = 0.010, n = 6 each). In contrast, differences in heart mass were not observed between Kvβ2-FTR and Kvβ2-sed animals (P = 0.878, n = 6 each). Histological analyses revealed greater cardiomyocyte cross sectional area in hearts of wt-FTR, but not in hearts from Kvβ2-FTR, animals compared with respective sed controls (P < 0.001; n = 6 each). Transcript abundance of Cited4 (inducer of physiological hypertrophy) was significantly greater (~45%; P = 0.024), while CEBP/β (growth repressor) and nfatc2 (inducer of pathological hypertrophy) were suppressed (~60%; P < 0.001, and ~35%; P = 0.033 respectively, n = 6 each) in wt-FTR relative to wt-sed hearts. However, these changes were absent in Kvβ2-FTR animals.Conclusions: Together, our data indicate an essential role for Kvβ2 in physiological cardiac growth in response to exercise conditioning.