Respiratory sinus arrhythmia (RSA) is the physiological increase in heart rate (HR) during inspiration and its decrease in expiration.

RSA is known to vary according to breathing frequency (f), although neither the mechanism nor the function of such correlation is clear.

Here, in young males and females breathing spontaneously or under auditory cues, we show that RSA correlates better with the HR–f ratio than with f alone, both under cortical or autonomic ventilatory drive.

This should imply that RSA is involved in the coupling of cardiac pulses and breathing acts, presumably to optimize gas exchange.