What? causes ?sinus arrhythmia?

Sinus node: Extra tissue around the sinus node or other abnormality causes the sinus node to contract abnormally. The sinus node s where the electrical signal for the heart to contract originates.

Atherosclerosis : The "pacemaker", the sino-atrial node, in the upper chambers of the heart (atria) lose control and other sites fire leading to irregular heartbeat.It is dangerous because it can cause turbulence in the blood flow leading to a clot.Other causes exist such as hyperthyroidism but usually decreased blood flow is the cause.

Usually normal. : The commonest type of sinus arrhythmia is related to breathing - also called respirophasic sinus arrhythmia. The hr speeds up during inspiration and slows during breathing out. This is normal, and a sign of good health. Rarely, sinus arrhythmia is seen in the elderly person, but without symptoms, it rarely requires treatment.