Okay, let me try to work through this question. The question is asking which of the options is not a feature of thyrotoxicosis. First, I need to remember what thyrotoxicosis is. It's a condition caused by excessive levels of thyroid hormones in the blood, leading to various symptoms.

So, the key here is to recall the common features of thyrotoxicosis. Common symptoms include weight loss despite increased appetite, heat intolerance, sweating, palpitations, tremors, anxiety, insomnia, and maybe some physical signs like goiter or exophthalmos. There's also a condition called thyrotoxic crisis, which is more severe.

Now, the options aren't provided, but the correct answer is supposed to be the one that's not a feature. Let's think about possible distractors. For example, constipation is a symptom of hypothyroidism, not hyperthyroidism. Hyperthyroidism usually causes diarrhea. So if one of the options is constipation, that's the exception. Another possible wrong option could be cold intolerance, which is also a feature of hypothyroidism. Weight gain would be another one. Fatigue might be a feature in hypothyroidism but not in thyrotoxicosis. Wait, but in thyrotoxicosis, patients often feel anxious and restless, so fatigue might not be a common symptom. However, some people might experience fatigue due to the body's overactivity. I need to be careful here.

Another point is that thyrotoxicosis can lead to atrial fibrillation, so palpitations are a feature. Also, heat intolerance is a key symptom. So if an option says cold intolerance, that's incorrect. So the exception is likely an option related to hypothyroid features. Let me check the possible wrong answers. If one of the options is constipation, that's not a feature. So the correct answer would be the one that's a symptom of hypothyroidism. Therefore, the question is testing the differentiation between hyper and hypothyroidism symptoms.

**Core Concept**
Thyrotoxicosis is characterized by elevated circulating thyroid hormones (T3/T4), leading to increased metabolic rate, sympathetic nervous system activation, and systemic effects. Key features include weight loss, heat intolerance, tremors, and tachycardia. Differentiating hyperthyroidism (e.g., Graves' disease) from hypothyroidism is critical.

**Why the Correct Answer is Right**
Cold intolerance is a hallmark of hypothyroidism due to reduced metabolic activity and impaired thermoregulation. In thyrotoxicosis, patients typically exhibit heat intolerance because excess thyroid hormones increase basal metabolic rate and heat production. This contrasts with hypothyroidism, where metabolic demands are low, leading to cold sensitivity.

**Why Each Wrong Option is Incorrect**
**Option A:** Heat intolerance is a classic feature of thyrotoxicosis, not an exception.
**Option B:** Tremors result from sympathetic overactivity in thyrotoxicosis, making this a defining symptom.
**Option C:** Tachycardia occurs due to increased β-adrenergic stimulation from elevated thyroid hormones.
**Option D:** Weight loss despite increased appetite is a cardinal sign of thyrotoxicosis.

**Clinical Pearl / High-Yield Fact**
Remember the "3 Hs"

✓ Correct Answer: A. Diastolic murmur