"an oleograph of the Sacred Heart over the mantelpiece"

An oleograph is a coloured lithograph made to look like an oil painting.

The Sacred Heart is a devotion* of the Catholic church to Jesus' physical heart, which is seen as representing his love for mankind. Traditionally, it has been an important theme in Christian Art.

*a form of prayer which is practised by some Catholics, but which is not an official part of the liturgy