I was playing Splinter Cell: Chaos Theory. Whenever the main character grabs people, he holds their wrists and they seem to be in a lot of pain. I went to a weblog and I was told that there was a meridian that related to the heart and lungs from the hands. Is this true?

Several! Within the first inch or two from the root of the hand.

They are (among others):
Lung:
Liehchueh (lung 7)
Chingchu (lung 8)
Yuchi (lung 9)
Heart:
lingtao (heart 4)
shenmen (heart 7)

they correspond to acupuncture. so find a chart and check the meridians.

Mind you I have not been able to use these effectively though I know they are used in several aikido (witch I practice) techniques like yonkyo nikyo and sankyo. So they take a lot of practice.

Are you claiming you can effect a person's heart or lungs by hitting their wrists?

I’m not going to get into the whole Chi (Ki, Qi etc.) philosophy. You'll have to ask acupuncturist. All I know is that these points hurt like h.. if hit right.

The heart and lung points on the wrist aren't meant to be hit. They simply need contact to work(grab,touch,press). They won't effect the heart or lung directly until other corresponding pressure points are hit.