Resistance to thyroid hormone (RTH) is a rare disease typically associated with elevated levels of thyroid hormones and non-suppressed thyroid stimulating hormones. The most common cause of RTH is thyroid hormone receptor β (THRβ) gene mutation. Most individuals with RTH are considered clinical euthyroid. We report a family with a rare heterozygous point mutation, c.959G>T, (p.R320L) of the THRβ gene. The proband developed atrial fibrillation and life-threatening heart failure with pulmonary edema, which was quite different from previously reported THRβ gene mutations. Considering the rareness of RTH and the heterogeneity of its phenotypes, our report allows for a better understanding of the manifestation and management of patients with RTH and THRβ gene mutation.