How high would your heart rate have to be to cause cardiac arrhythmia or cardiac arrest?

Arrythmia heart arre: You have actually two questions.Heart rhythem problems are of two kind one is when heart is beating faster then it should and second is when heart is beating slower then normal rate.They are due to disruption of normal heart rhythm.Heart rate above 120 and below 60 are the one we are cocerned and we check on ekg.Cardiac arrest is when heart stop beating and lot of time it is fatal and is emmergenc.

Not so simple: Arrythmia is not defined by the heart rate. The arrhythmia refers to a disturbance in the way the electrical impulse is generated and transmitted inside the heart. Extremes of slow and rapid heart rate are equivalent to a cardiac arrest since in these instances the heart is not pumping enough blood to maintain an effective blood pressure.

Depends...: There are heart rhythmn disorders that do not begin with an elevated heart rate. Not all cardiac arrhythmias are due to an elevated heart rate. There are rhythmn disorders that have a normal heart rate or even a slow heart rate. A normal or slow heart rate does not rule put an arrhythmia.