an apparatus for isolating a first zone from a second zone in a subterranean wellbore . the apparatus includes an outer tubular and an inner tubular disposed within the outer tubular forming an annular flow path therebetween that is in fluid communication with the first zone . the inner tubular defines a central flow path that is in fluid communication with the second zone . a sleeve having at least one seal is positioned in the annular flow path and is axially movable relative to the inner and outer tubulars between a closed position wherein the seal engages the inner tubular and an open position wherein the seal engages the outer tubular . a mandrel is slidably disposed within the inner tubular and is coupled to the sleeve . the mandrel is operable to shift the sleeve between the open position and the closed position responsive to changes in pressure within the central flow path .