© 2021, Republic of China Society of Cardiology. All rights reserved.Objectives: Exposure to arsenic is associated with various cardiovascular diseases. The imbalance between antioxidant and oxidant homeostasis plays a crucial role in the cardiovascular effects of arsenic. The aim of this study was to investigate the effect of arsenic exposure on diastolic function by measuring thiol and disulphide in arsenic-exposed workers. Methods and Results: A total of 107 male arsenic-exposed workers and 36 healthy subjects were enrolled. Mitral inflow velocity and parameters of diastolic function were measured. As oxidative stress indicators, total thiol, native thiol, disulphide, and their percent ratios were determined. The mean age was 39.1 ± 9.5 years in the arsenic-exposed group and 37.4 ± 9.6 years in the controls. The median blood arsenic level was 42 μg/dL in the arsenic-exposed group and 3.75 μg/dL in the controls. E-wave, E/A ratio, and e' wave were lower and left atrial diameter, A-wave, average E/e' ratio, and tricuspid regurgitation velocity were higher in the arsenic-exposed group. Native and total thiol concentrations were lower, and disulphide/native and disulphide/total thiol ratios were higher in the arsenic-exposed group. Fourteen (13.1%) workers had diastolic dysfunction, 26 (24.3%) had indeterminate, and 67 (62.6%) had normal diastolic function, compared to 1 (2.8%), 2 (5.6%), and 33 (97.7%) in the control group, respectively. In regression analysis, disulphide/native thiol ratio (p < 0.001) and blood arsenic level (p < 0.001) predicted increased average E/e' ratio in the arsenic-exposed group. Conclusions: This study showed strong associations among arsenic exposure, oxidative stress, and diastolic function, and revealed the influence of arsenic exposure on diastolic dysfunction through oxidative stress.