56 y/o F h/o CHF (EF 20-25%), rheumatic heart dz w/ severe mitral stenosis and regurg presents with

56 y/o F h/o CHF (EF 20-25%), rheumatic heart dz w/ severe mitral stenosis and regurg presents with acute onset SOB and light headedness.

Top EKG– before.
Bottom EKG after metoprolol and cardizem.

Diagnosis?