Endomyocardial biopsy
Biopsy sampling fo the myocardium has been done using needles which produced suboptimal samples. The advent of the bioptome allowed safe sampling and produced excellent tissue samples with high reproducibility once an operator becomes experienced in obtainin the samples. For the pathologist this type of sample procures excellent material from the subendocardial (trabecular) myocardium.
The absence of cellular rejection is called Grade 0R and and example is shown below.
In Grade 0 R there is no evidence of mononuclear
(lymphocytes / macrophages) inflammation or myocyte
damage. 
