Environmental asbestos exposure is related to diffuse pleural disease (thickening and calcification) and restrictive pulmonary disease. To assess cardiac autonomic system, we investigated the time domain heart rate variability (HRV) by Holter monitoring and their correlation with pulmonary function tests in patients with pleural disease caused by environmental asbestos exposure. We studied 45 patients (26 men, 19 women, aged 62.67 +/- 10.1 years) and 35 healthy patients who had similar sex and age profile to the patients (24 men, 11 women, aged 59.31 +/- 8.4 years). The asbestosis group was divided into 3 subgroups according to the severity of forced vital capacity (FVC) severe (group 1) (n = 12): FVC less than 50% of expected, moderate (group 2) (n = 16): FVC 64%-51% of expected and mild (group 3) (n = 17): FVC 65%-80% of expected. HRV parameters were significantly different among all groups (P < .0001). Comparing the 4 groups (subgroups and control group), group 1 had the lowest mean HRV values and controls had the highest mean HRV values (P < .0001). Severity of autonomic dysfunction was correlated with the severity of FVC and arterial oxygen pressure. Right ventricular end-diastolic internal diameter (RVEDID) and right ventricular end-systolic internal diameter (RVESID) values were significantly increased in patients ( P < .0001, P < 0.0001, respectively). Pulmonary acceleration time (AcT) values were shorter in all patient groups than control group (P < .0001). It was shortest in group 1. Group 2 and 3 had shorter AcT values than control group. HRV parameters were correlated positively with AcT values and negatively with RVEDID and RVESID values. In conclusion, patients with restrictive pulmonary disease due to environmental asbestos exposure had autonomic dysfunction, which was correlated with the severity of restriction. This was thought to be the result of chronic hypoxia, pulmonary hypertension, and right ventricular enlargement.