A 30-year-old woman presents with fatigue and palpitations on exertion for over a year. Physical examination reveals conjunctival and lip pallor, heart rate of 110 bpm, and a grade II systolic murmur at the apex. Laboratory tests show hemoglobin (Hb) 60g/L, mean corpuscular hemoglobin concentration (MCHC) 0.25 g/dl, mean corpuscular volume (MCV) 70μm³, serum iron 6.2μmol/L, serum transferrin saturation 10%, and total iron-binding capacity (TIBC) 3690μmol/L. The most likely diagnosis is: