A downhole impact apparatus operable to impart an impact to an object within a wellbore. The impact apparatus may include a housing, a first chamber within the housing, a second chamber within the housing, and a piston assembly slidably disposed within the housing. The piston assembly may include a first piston slidably disposed within the first chamber and dividing the first chamber into a first volume and a second volume, a second piston slidably disposed within the second chamber, and a shaft connecting the first and second pistons. The first volume may be open to a space external to the housing and the second volume may be fluidly isolated from the space external to the housing. Relative movement between the piston assembly and the housing ends with the impact. The second chamber may be configured to contain a fluid to prevent relative movement between the piston assembly and the housing.