Which arrhythmia is characterized by a racing heart rate of more than 100 bpm?

Tachycardia is characterized by a racing heart rate exceeding 100 beats per minute. This condition can arise due to various factors, including increased sympathetic nervous system activity or underlying heart conditions. It is essential to recognize that while there are different types of tachycardia, the defining feature is the elevated heart rate.

In the context of this question, atrial fibrillation is marked by an irregular and often rapid heart rate but does not specifically categorize the heart rate purely based on the numeric threshold. Bradycardia, on the other hand, indicates a slower than normal heart rate, typically below 60 beats per minute. Ventricular fibrillation, a serious condition, involves chaotic electrical activity leading to ineffective heart contractions, but it does not define a specific heart rate in the same way that tachycardia does.

Thus, tachycardia distinctly applies to the situation described, where the heart rate is increased beyond the standard threshold of 100 bpm, making it the correct answer.