Step 1: Understanding the Concept
Noise causes sleeplessness, altered breathing, increased heartbeat, and stress.
Step 2: Key Point
Heartbeat increases with noise, it does not decrease.
Step 3: Compare the options
So the exception is decreased heartbeat.
Final Answer:
Noise does not cause decreased heartbeat.
\[ \boxed{\text{(B) }\text{decreased heartbeat}} \]