Thyroid Hormone Replacement for Subclinical Hypothyroidism and Chronic Heart Failure (ThyroHeart-CHF)

Inclusion Criteria:

• Aged 18 years or older, male or female.

• Systolic heart failure with New York Heart Association (NYHA) class II-III.

• Left ventricular ejection fraction (LVEF) less than 40% by echocardiography duringscreening and randomization.

• SCH (TSH: upper limits of normal (ULN) -10mIU/L, and FT4 level within referencerange).

• Having received standard HF therapy for at least 2 weeks, having reached target doseor max tolerable dose.

• Provided informed consent.

Exclusion Criteria:

• Acute heart failure or acute exacerbation of chronic heart failure within the past 2weeks.

• Scheduled cardiac resynchronization therapy or heart transplantation.

• History of malignant tumor or life expectancy under 12 months.

• Already on medications that may affect thyroid function (L-T4, carbimazole,propylthiouracil, amiodarone, lithium).

• Pregnancy and lactation period.

• Participation in another clinical trial within the past 30 days.

• Contraindication or intolerance to evidence-based therapy for CHF, such asbeta-blocker, angiotensin-converting enzyme inhibitor or angiotensin receptor blocker.

• Known hypersensitivity to the trial treatment(s) or diluents (when applicable),including placebo or other comparator drug(s).

• Untreated adrenal insufficiency.

• Untreated pituitary insufficiency.

• Untreated thyrotoxicosis.

• Treatment with levothyroxine must not be initiated in patients with acute myocardialinfarction, acute myocarditis, or acute pancarditis.

• Severe renal dysfunction (eGFR≤30 ml/min/1.73m2).

• Significant hepatic impairment (Serum GPT > 120 U/L).

• Any disorder which, in the opinion of the investigator, might jeopardise subject'ssafety or compliance with the protocol.