The relationships between road and rail traffic noise with pre-ejection period (PEP) and with respiratory sinus arrhythmia (RSA) during sleep, as indices of cardiac sympathetic and parasympathetic nervous system tone, were investigated in the field (36 subjects, with 188 and 192 valid subject nights for PEP and RSA, respectively). Two analyses were conducted. The first analysis investigated the overall relationships across the entire sleep period. A second analysis investigated differences in the relationships between the first and second halves of the sleep period. Separate multilevel linear regression models for PEP and RSA were employed. Potential covariates for each model were selected from the same pool of variables, which included: gender, age, body-mass index, education level, traffic noise source type, intake of medication, caffeine, alcohol and cigarette smoke, and hindrance during sleep due to the ambulatory recordings. RSA models were adjusted for respiration rate. Mean indoor traffic noise exposure was negatively related to mean RSA during the sleep period, specifically during the second half of the sleep period. Both respiration rate and age were negatively associated with RSA. No significant relationships were observed for PEP. The results indicate that higher indoor traffic noise exposure levels may lead to cardiac parasympathetic withdrawal during sleep, specifically during the second half of the sleep period. No effect of indoor traffic noise on cardiac sympathetic tone was observed.