For All Hearts, except chicken hearts: Trim the hard, white exterior fat and any visible membranes with a sharp paring knife, and cut out visible arteries, veins, or other non-muscle meat from the top of the heart, then rinse thoroughly with cold water. You should end up with a piece of relatively smooth, blood-red muscle meat. (Any further cutting or prep would be individual to the recipe.)
Note that most larger animal hearts will be sourced from a local farm and butcher, and you’ll notice they have already been cut or sliced open for quality control (to ensure the organ is healthy and safe and didn’t contain any bugs or parasites.)
For Chicken Hearts: Chicken hearts can be purchased at many grocery stores. They tend to be already cleaned and removed of any excess material and are generally ready to cook after being rinsed thoroughly in cold water. (Pro Tip: Squeeze the hearts while rinsing to ensure you get rid of trace amounts of blood inside them.)
This information is an excerpt from It Takes Guts by Ashleigh Vanhoute and can be purchased here.