Which of the following is NOT a cause of tachycardia?

Tachycardia refers to an elevated heart rate, typically defined as a resting heart rate exceeding 100 beats per minute. It has various physiological triggers, including stressors to the body that provoke a response to increase blood flow and oxygen delivery.

Bradycardia, which is characterized by a slower heart rate (typically less than 60 beats per minute), is fundamentally the opposite of tachycardia. While pain, hypoxia, and dehydration can all lead to increased heart rates as compensatory mechanisms—pain through stress response, hypoxia through increased demands for oxygen, and dehydration as a response to lowered blood volume—bradycardia does not promote an elevated heart rate. Instead, it indicates that the heart is beating slower. Thus, bradycardia is not a cause of tachycardia, making it the correct choice in identifying what does not contribute to an increased heart rate.