A downhole pressure isolation tool is disclosed for use in a tubing string or casing string. The tool includes a frangible disk or seal within a housing having a bore. The disk has a dome section and a cylinder section and the dome of the disk is transverse to the bore. A piston is located between the housing and the cylinder of the disk, the piston movable between a first position and a second position, the second position, engaging a set of fingers which push into the cylinder of the disc to break it, causing the entire disk the cause and the entire disk to fail. A rupturable membrane is provided which, when it ruptures places the piston in fluid communication with a fluid within the bore.