Which of the following is a contraindication for an exercise ECG test?

Unstable angina is indeed a contraindication for an exercise ECG test because this condition indicates that the patient's chest pain is unpredictable and occurs at rest or with minimal exertion, suggesting that the heart is under significant stress. Performing an exercise ECG could increase the risk of serious complications, such as a myocardial infarction, as it would impose additional physical stress on the heart during a time when it is already compromised.

In contrast, stable angina typically allows for physical exertion as the symptoms are predictable and occur under controlled settings, making it safer for exercise testing. Chronic fatigue syndrome does not inherently contraindicate exercise testing, and although hypertension is a consideration, it is generally not an outright contraindication unless it's severely uncontrolled. Each of these other conditions can be managed more safely in a controlled setting, unlike unstable angina, which poses immediate risks during an exercise stress test.