**Core Concept**
Ischemic heart disease (IHD) and hypothyroidism often coexist, and thyroid hormone replacement therapy can have significant effects on cardiovascular function. The underlying principle being tested here involves the complex interplay between thyroid hormones and cardiac function.

**Why the Correct Answer is Right**
Thyroid hormones play a crucial role in regulating cardiac function, including increasing contractility and heart rate. In patients with hypothyroidism, the decreased levels of thyroid hormones can lead to decreased cardiac output, which may worsen IHD symptoms. Therefore, the most appropriate line of management would be to initiate thyroid hormone replacement therapy to normalize thyroid hormone levels, thereby improving cardiac function and potentially reducing IHD symptoms.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not address the underlying issue of hypothyroidism, which may be exacerbating IHD symptoms.
**Option B:** This option is incorrect because it may not be necessary in this scenario, and the patient's IHD symptoms may not be adequately managed without addressing the hypothyroidism.
**Option C:** This option is incorrect because it does not take into account the potential benefits of thyroid hormone replacement therapy on cardiac function.

**Clinical Pearl / High-Yield Fact**
Thyroid hormone replacement therapy can significantly improve cardiac function in patients with hypothyroidism, but it should be initiated under close monitoring to avoid exacerbating IHD symptoms.

**Correct Answer:** D.