MP3 Player Shield plays sound, Arduino waits for the sound to finish?

When the arduino sends out a signal to the mp3 player shield, arduino waits for the sound to be played and doesn't continue directly. How can that be solved?

Thanks!

What make and model MP3 shield are you using?

Are you using a library to access the hardware?

If so, what library?

What code are you using to initiate the playing?