A 35-year-old male presents with lower extremity edema, oliguria, and shortness of breath for 2 months. Physical examination reveals jugular vein distension, few basal crackles in the lungs, cardiomegaly, heart rate 100 bpm with regular rhythm, audible S2, and a 2/6 systolic blowing murmur at the apex. The liver is palpable 3 cm below the costal margin, and lower extremity edema is present. Echocardiogram shows cardiac enlargement with diffuse hypokinesis of the ventricular walls, and urinary protein is positive. The most likely diagnosis is: