What is the recommended method for cannulating isolated hearts from small animals?

Firstly, the heart must be removed from the chest cavity of the animal using either of two surgical procedures:

  1. Median sternotomy: An incision is made along the sternum, after which the sternum itself is divided (or "cracked") to expose the heart; OR
  2. Bilateral sternotomy: Two incisions are made on both sides of the sternum to expose the chest cavity.
    After successful extraction, the heart is then immersed in an ice-cold solution or semi-frozen solution.

The heart is then cannulated using one of the two following methods:

  1. The Vertical method: The aorta is identified while the heart is maintained on an ice-bed. The aorta is then quickly cannulated without the use of a microscope. The aorta is then clipped onto the cannula for support before tying it off with a suture (thread). It is recommended that the researcher keep a container of semi-frozen solution in close proximity to maintain the heart during the cannulation process. 
  2. The Horizontal method: The cannula (previously filled with perfusate using a three-way tap) is detached from the perfusion system and attached to a micro-positioner. The micro-positioner is then used to manouver the cannula horizontally above the heart. The aorta is identified under a microscope and then cannulated while lying on an ice-bed. After the aorta is cannulated, the heart and the cannula are reattached to the perfusion system. Care must be taken to ensure no air bubbles enter the perfusion system.