Yes, PACEMAKERS is a Scrabble word!

Letter values in Scrabble US: P 3, A 1, C 3, E 1, M 3, A 1, K 5, E 1, R 1, S 1.

Is it a valid word?

PACEMAKERS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a leading instance in its field
a specialized bit of heart tissue that controls the heartbeat
an implanted electronic device that takes over the function of the natural cardiac pacemaker
a horse used to set the pace in racing

Also: cardiac pacemaker, sinoatrial node, sa node, artificial pacemaker.