how much to bet

[holdemplayer111]

lets say i have something like ace king, and the flop comes A [img]/images/graemlins/spade.gif[/img] 5 [img]/images/graemlins/heart.gif[/img] 9 [img]/images/graemlins/heart.gif[/img]. i am up against one opponent, and i read him to have the flush draw, but at the moment i think i have the best hand,but i don't have a heart in my hand. how much should i bet in this situation to make it to expensive for him to draw at the flush. also, does the same apply for a straight draw? thanks for the help