I have experience doing this with LV tissue, but I have never tried in RV. I usually cut transverse (short axis) across the LV at the mid-papillary level, so that the cardiomyocytes align well and it makes the staining with picrosirus red look uniform. I assume this is much harder to do in RV tissue, as it is much thinner and doesn't form a natural ring shape.

Does anyone have experience with sectioning the RV as a flat sheet?