Cardiac arrhythmia

Some arrhythmiae are life-threatening medical emergencies that can cause cardiac arrest and sudden death. Others cause aggravating symptoms, such as an awareness of a different heart beat, or palpitation, which can be annoying. Some are quite small and normal. Sinus arrhythmia is the mild acceleration followed by slowing of the normal rhythm that occurs with breathing. In adults the normal resting heart rate ranges from 60 beats per minute to 100 beats per minute. The normal heart beat is controlled by a small area in the upper chamber of the heart called the sinoatrial node or sinus node. The sinus node contains specialized cells that have spontaneous electrical activity that starts each normal heart beat.