**Question:** The frequency of the first heart sound (S1) is:

A. 60 Hz
B. 80 Hz
C. 100 Hz
D. 120 Hz

**Core Concept:**
First heart sound (S1) is the result of the closure of the tricuspid and pulmonary valves, which occur simultaneously. S1 is generally considered to be a result of the combination of the closure of the atrioventricular (AV) valves - tricuspid and pulmonary valves.

**Why the Correct Answer is Right:**
The correct answer is **D. 120 Hz**. This is because S1 is the result of the closure of both the tricuspid and pulmonary valves, which occur approximately twice per cardiac cycle. In humans, the heart rate averages around 60-100 beats per minute (bpm), and thus, the frequency of S1 is calculated as follows:

S1 frequency = Heart rate × 2
S1 frequency = 60 bpm × 2 = 120 Hz

**Why Each Wrong Option is Incorrect:**

A. 60 Hz - This is too low as the heart rate is typically higher than 60 bpm.
B. 80 Hz - This is still too low as the heart rate can be significantly higher than 80 bpm.
C. 100 Hz - This is too high as the frequency of S1 should be directly proportional to the heart rate, not twice the value.

**Clinical Pearl:**
Understanding the frequency of the first heart sound (S1) is crucial in assessing cardiac health. A decrease in S1 frequency could indicate a reduced heart rate or heart valve abnormalities, while an increase in S1 frequency could suggest tachycardia (rapid heart rate). Additionally, the frequency of S1 can give insights into the overall cardiac function and health.