We image macroscopic transient pores in mechanically stretched giant vesicles. Holes open above a critical radius rc1 , grow up to a radius rc2 , and close. We interpret the upper limit rc2 by a relaxation of the membrane tension as the holes expand. The closing of the holes is caused by a further relaxation of the surface tension when the internal liquid leaks out. A dynamic model fits our data for the growth and closure of pores.