A “Sinus Arrhythmia” is a normal speeding of the heart rate that happens during inspiration. Though it sounds pathological, it functions in all humans at all times. This is a natural response and is more commonly seen in children than adults.

This is not a true “arrhythmia”. It is caused by a slight increase in the heart rate due to sympathetic stimulation of the Sinoatrial (SA) Node due to inspiration. A slight decrease in pacing rate by the parasympathetic system inhibits the SA Node during expiration. (6)

On an EKG, you will see the R-R interval is variable when a sinus arrhythmia is present.

This condition is rarely ever pathologic and can be an indirect measure of vagal tone, as vagal tone goes up, this phenomenon is seen more frequently. (4)

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