The psychophysiological literature on mental effort is dominated by cardiovascular and pupil-related measures. However, research has not yet systematically compared effort-related cardiovascular and pupillary correlates of effort albeit both types of measures being driven by the same autonomic mechanisms. The presented study closed this gap by examining sympathetic and parasympathetic responses at the level of two organs—the heart and the pupil—to changes in the difficulty of a speech-in-noise task. Ninety-six participants performed twenty-six trials of the task under four different signal-to-noise ratios—ranging from -12dB to -6dB. In each trial, three digits embedded in white noise were presented, and participants had to repeat the presented digits. Participants performed the task twice under two different room light conditions—in the dark and with normal room light—to disentangle the sympathetic and parasympathetic contributions to changes in pupil diameter. Pre-ejection period, respiratory sinus arrhythmia, and pupil diameter were assessed during the tasks and preceding baseline (rest) periods to quantify sympathetic and parasympathetic responses to changes in listening demand. The results revealed that sympathetic impact on both the heart and the pupil dominated the respective parasympathetic effects suggesting that similar autonomic mechanisms underlie the responses of cardiac and pupillary correlates of mental effort.