[Histonet] Cracking tissue

[Solverboy <@t> aol.com]

Hello All,
   I am cutting transverse sections of fixed, frozen rat heart on a cryotstat.  When I mount my sections immediately after cutting, the histology looks perfect, but within two minutes of warming(room temp.) onto Fisherbrand Superfrost Plus slides, the tissue begins to crack (more specifically the muscle fibers tend to seperate from one another).  Does anyone know a solution to or a cause of this problem?  

Thanks in advance,

Frederic Grau
Dept. Neurobiology & Behavior
S.U.N.Y. Stony Brook