Try triphenyltetrazolium chloride on slices of fresh,
unfixed heart. Here are a couple of refs that came easily
to hand. Other tetrazolium salts are also used for this 
purpose, and it would be possible to make a long list.
Mitochondrial activity in living tissue reduces tetrazolium
salts to coloured formazans. This is a sensitive way to
detect dead patches in an organ. Richard Horobin's chapter
(13) in the 10th edn of Conn's Biological Stains has more
explanations and lots of very recent refs for all the 
tetrazolium salts used in exptl biology, histochemistry 
etc etc.

My 2 refs:

Holmbom B, Naslund U, Eriksson A, Virtanen I, Thornell LE (1993)
Comparison of triphenyltetrazolium chloride (TTC) staining versus
detection of fibronectin in experimental myocardial infarction.
Histochemistry 99: 265-275.

Bednar MM, Fanburg JC, Anderson ML, Raymond SJ, Dooley RH, Gross
CE (1994) Comparison of triphenyltetrazolium dye with light
microscopic evaluation in a rabbit model of acute cerebral
ischaemia. Neurological Research 16: 129-132.

Hope this helps. You could also try PubMed or Web of Science,
and get more references than it's feasible to read!

If you have already fixed the specimens, you could simply
stain them with any method that includes an anionic dye, such
as Giemsa, acid fuchsine & toluidine blue, or even H&E. Recently
dead cells are more strongly acidophilic than healthy ones.
This is traditional wisdom, and it has some support from 
histochemical investigations, but in the brain rather than the
heart. (See: A histochemical examination of the staining of 
kainate-induced neuronal degeneration by anionic dyes. 
Biotechnic & Histochemistry 73, 244-254.)
-- 
-------------------------
John A. Kiernan
Department of Anatomy and Cell Biology
The University of Western Ontario
London,   Canada   N6A 5C1
   kiernan@uwo.ca
   http://publish.uwo.ca/~jkiernan/
___________________________________________________
> KC Rosburg wrote:
> 
> Greetings fellow Histonetters
> 
> I have a investagator that is looking for the best way to
> locate a infarct in a mouse heart, a trichrome was suggested
> but does any one know of another way to detect infarcts.  I.E.
> what to look for in the sample or best stain.  It is more
> difficult since the hearts are only kept alive for 12 hours
> after the infarct, which is too early for a collagen type
> stain.  There is alot of hearts and to have to stain them twice
> seems to be alot of work that might be able to be avoided
> 
> Thanks
> Kris
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