I can recommend the Qiagen miRNEasy kits for total RNA extraction from cardiac tissue. I generally mince or crush the tissue before homogenization in Qiazol.

Qiagen has the RNeasy Fibrous Tissue extraction kit which is perfect for cardiac tissues.

You can purchase metal beads that are 5 mm in diameter and range free. The heart is placed in a 1.5 ml screw top tube with o-ring and about .75 ml of beads and then topped off with trizol reagent and the lid is then screwed shut. The samples are then placed in an agitator so that the meads macerate the tissue. Generally about 4 min. The slurry of trizol is then used to isolate the rna. It is important to do this quickly and to keep reagents cold.