Thaw heart upside down in glass bowl or measuring cup. This will help liquid drain out of the heart.
Trim all outer fat from the heart using a filet/boning knife. Cut vessels from the top of the heart.
With the bottom of the heart (pointed end) facing towards you, run your knife along the vessel that runs diagonally across the front of the heart. Continue cutting until you remove the entire piece of muscle. This is the left ventricle.
Once the left ventricle is removed, run your knife under the piece of muscle that was under the ventricle. Continue cutting until the entire heart is opened into one flat piece.
Trim strings from inside the heart and remove anything else that's not muscle.
Cut meat into ½" strips.
In a glass storage container or medium bowl, combine soy sauce, sesame oil, rice vinegar, brown sugar, ½ cup green onions, garlic, ginger, and sesame seeds. Place meat in marinade and stir to coat the meat.
Cover and refrigerate for 3-12 hours.
Soak wooden skewers in warm water for 30 minutes or use metal skewers.
Place meat on skewers in an accordion style and spread the meat out so that you can see the skewers between the meat.
Preheat grill to 350°F. Grill for 2-3 minutes per side or until outsides are lightly charred and the inside is still moist and tender.
While steak is cooking, pour remaining marinade into a small saucepan. Bring to a simmer and simmer until reduced and thickened slightly. (optional)
Top with sliced green onions and serve with reduced marinade, if desired. Enjoy!
Notes
This recipe works with any big game heart (deer, elk, moose, antelope, beef, etc.) or several small game/game bird hearts. It also works great with strips of any type of steak you want!
If there is any coagulated blood left on the inside of the heart that you can't remove, rinse the meat with cold water to clean it out. Typically, I wouldn't suggest rinsing meat. But with hearts, it can sometimes be necessary to remove all of the blood and reduce the iron taste of the meat.
Don't overcook the meat. Like any venison steak, deer heart is lean and will lose its natural moisture when it is overcooked.