Which of the following is a symptom of heat exhaustion?

Heavy sweating with cool, clammy skin is indeed a symptom of heat exhaustion. This condition occurs when the body becomes overheated, typically due to prolonged exposure to high temperatures and physical exertion. The heavy sweating is the body's attempt to cool itself down, while the cool and clammy skin indicates that the body is losing moisture and may be struggling to maintain an adequate temperature regulation.

In the context of heat-related illnesses, heat exhaustion typically manifests before heat stroke, which can be much more severe. Recognizing the early symptoms, such as cool, clammy skin and heavy sweating, allows for timely intervention to prevent progression to heat stroke, which is characterized by fever and potentially dry skin due to the body's inability to sweat effectively.

The other options describe symptoms that align more with other conditions or later stages of heat-related illnesses. For instance, high fever and rapid heartbeat are more indicative of heat stroke rather than heat exhaustion. Extreme fatigue without sweating could indicate heat stroke or other medical conditions. Lastly, an intense headache and visual disturbances can also arise from dehydration or heat stroke, but they are not typical markers of heat exhaustion.