During a heart attack, the affected person should be instructed to:

During a heart attack, it is crucial to prioritize the affected person's safety and comfort. Instructing them to rest quietly minimizes physical exertion, which can further strain the heart. Chewing ASA (acetylsalicylic acid, commonly known as aspirin) is an important step, as it can help thin the blood and improve blood flow, potentially reducing the severity of the heart attack.

Resting helps to lower the heart's demand for oxygen, which is critical during this emergency. Meanwhile, the action of chewing aspirin allows for quicker absorption into the bloodstream, enabling it to work more effectively.

This approach emphasizes the significance of not only reducing physical activity but also addressing the cardiac emergency with appropriate medications while waiting for professional help. The other options, which suggest walking, consuming water, or taking a shower, do not align with the necessary immediate response during a heart attack, as they may escalate the risk and complicate the situation.