A gas turbine engine combustion chamber includes a first wall and a second wall. The second wall is arranged within and spaced from the first wall to define a cavity between the first wall and the second wall. The first wall has a plurality of impingement apertures extending there-through and the second wall has a plurality of effusion apertures extending there-through. The impingement apertures have a first diameter, a first pitch, and a first area. The effusion apertures have a second diameter, a second pitch, and a second area. The ratio of the first diameter to the second diameter is at least 3, the ratio of the first pitch to the second pitch is at least 4 and the ratio of the first area to the second area is at least 9. This arrangement increases the cooling performance of the effusion apertures in the second wall.