Yes, CARDIOGRAPH is a Scrabble word!

Letter values in Scrabble US: C 3, A 1, R 1, D 2, I 1, O 1, G 2, R 1, A 1, P 3, H 4.

Is it a valid word?

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

medical instrument that records electric currents associated with contractions of the heart
a medical instrument that measures the mechanical force of cardiac contractions and the amount of blood passing through the heart during a specified period by measuring the recoil of the body as blood is pumped from the ventricles

Also: electrocardiograph, ballistocardiograph.