arrhythmia

n. irregular heartbeat (Medicine)

Cardiac arrhythmia is any of a group of conditions in which the electrical activity of the heart is irregular or is faster or slower than normal. Some arrhythmias 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 minor and can be regarded as 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.
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Arrhythmia /ar·rhyth·mia/ variation from the normal rhythm of the heartbeat, encompassing abnormalities of rate, regularity, site of impulse origin, [more]Arrhythmia - Community and Resources

Noun
1. an abnormal rate of muscle contractions in the heart
(synonym) cardiac arrhythmia
(hypernym) heart disease, heart condition, cardiopathy
(hyponym) flutter

noun
variation in the rhythm of the heartbeat
see also ANTI-ARRHYTHMIC
QUOTE:Cardiovascular effects may include atrial arrhythmias but at 30ºC there is the possibility of spontaneous ventricular fibrillation British Journal of Nursing