<prompt> Sinus arrhythmia is due to-Sinus node diseaseExaggerated response to sympathetic systemFluctuating parasympathetic response during respirationDecreased hea rate in inspiration  <response>: Answer-C. Fluctuating parasympathetic response during respirationSinus rhythm with a beat-to-beat variation in the P-P interval the time between successive P waves, producing an irregular ventricular rate.Sinus arrhythmia is a normal physiological phenomenon, most commnonly seen in young, healthy people.The hea rate varies due to reflex changes in vagal parasyntpathetic tone during the different stages of the respiratory cycle,Inspiration increases the hea rate by decreasing vagal tone.With the onset of expiration, vagal tone is restored, leading to a subsequent decrease in hea rate. 