Which of the following indicates a slow heart rate?

Bradycardia is the term that refers specifically to a slow heart rate, generally defined as a resting heart rate of fewer than 60 beats per minute in adults. It is important in clinical settings because it can indicate underlying health issues, such as heart block, electrolyte imbalances, or may arise as a response to certain medications.

In contrast, the other terms do not describe a slow heart rate. Hypertension refers to high blood pressure and does not pertain directly to heart rate. Tachycardia indicates a fast heart rate, typically over 100 beats per minute, which is the opposite of bradycardia. Arrhythmia refers to any irregularity in the heartbeat which could include fast, slow, or uneven heart rates. Therefore, while all these terms relate to heart function, bradycardia is the only one specifically indicating a slow heart rate.