FORENSIC on stab wounds to the heart...

Chest wounds bleed pretty quickly, but they do so internally, making them almost more fatal than other types of stab wounds. If someone is stabbed anywhere in the heart, what usually happens is that either the lining of the heart or the chest cavity itself fills with blood. This can kill the person in anywhere from 10-15 seconds to a couple of minutes.

Lateral chest - out toward the side. Right side's less tricky than the left. At or slightly below the level of the nipple. Most likely he'll end up with a collapsed lung which can be treated with a chest tube to re-inflate it.

http://www.dundee.ac.uk/forensicmedicine/notes/woundsdjp.pdf