How long after a donor dies can the organs still be used?
An cadaverous organ donor can either be a "heart-beating donor"
(aka, brain dead) or a "non-heart beating donor". Those in the
first category have suffered a severe head injury, meaning they
will never regain consciousness or recover, but their heart is
still pumping blood around their body. Whereas those in the other
group have suffered some event which has stopped their heart - e.g
a sudden cardiac arrest.
Those in the "non-heart beating donor" category are never used
for heart transplants, since their heart has been the cause of
their death; their heart does not work.
Only those in the "heart-beating donor" category are used for
heart transplants; in these donors, the heart does not stop beating
until it is removed from their body - the heart is not "dead" as
such, but the donor is brain dead so has no use for a functioning
heart. And just because the heart ceases to beat when outside of
the body does not mean it is "dead".
Possibly your question should be "how long do you get between
harvesting a heart for transplant until it becomes unusable?",
since using a "dead" heart for a transplant would be utterly
pointless. However, if that was your question, you get around 4-5
hours.