can't use iMac 27 mid 2010 - yosimte- as display target with with mac pro 2009 - maviricks - altho i use mini display cdmi caple

i have imac 27 inch mid 2010 and i try to use it as display target with mac pro 2009 and i make the step open the two computer and connect together with mini display - hdmi - cable but didn't detect

i mac have os x yosimete and mac pro have mavericks