Drug S is most like: (A) Epinephrine, (B) Isoproterenol, (C) Norepinephrine, (D) Phenylephrine
Answer is B. The effects of Drug S are changed by treatment with the beta blocker, but not by the alpha blocker (choices A, C, and D are ruled out). Terbutaline is beta2 selective and would not increase heart rate directly. Drug S is isoproterenol.