Sinus arrhythmia is a small difference in cycling of the sinus rhythm, normally it goes beyond 0.12 seconds between the longest and smallest cycles. Sinus arrhythmia is a common in kids and young adults because allergies can easily hit them as their immune system is not that strong as adults. It normally lessens or disappears with age. Sinus arrhythmia is often somewhat more frequent with vacillation in the respiratory cycle as heart rate goes faster with inhale and slows with exhale. Sinus arrhythmia might be provoked by any factor that boosts vagal tone.
