If the beef heart is frozen, thaw overnight in the refrigerator or under cool running water until thawed.
Steam or gently simmer the whole, unpeeled russet potatoes until completely cooked. You can check if the potato is done if a skewer easily punctures the whole potato. This will take 1- 1.5 hours. I prefer steaming because the potatoes are less likely to break apart. When the potatoes are done cooking, allow the potatoes to cool in the fridge for at least 1 hour or up to overnight.
Soak the ancho chili in boiling water for 10 minutes.
Soak 6-10 wooden skewers in water for at least 30 minutes, keep them soaking until you are ready to skewer the meat.
Note that there are 2 openings (ventricles) in each heart. Try to cut the heart in 3 flat pieces. Two pieces from either side of the heart, and one piece that is the muscle in between the two ventricles. If you have trouble, don't worry because you will be cutting the heart into small chunks anyways.
Here I have removed one side of the heart.
Here I am separating the other side of the heart from the muscle in between the two ventricles.
Take each piece of heart (it doesn't matter how many pieces you ended up with), and use a sharp knife to "shave" away the gnarly-looking, veiny, inner part of the heart.
The heart should look like smooth muscle when you are done.
flip the heart over and cut away any fat on the outside of the heart. If you can carefully peel away the very outer membrane of the heart, awesome. If not, no big deal.
Repeat this process with the rest of the pieces of heart until they look like clean pieces of meat.
Cut the beef heart into chunks that are roughly 1.5 inches long and wide but no more than 1/2 inch thick. Set the heart pieces aside in a mixing bowl.
Remove the ancho chili from the water it was soaking in (discard the soaking water) and place it into the blender with all of the rest of the ingredients listed under "anticuchos" above (not including the heart, obviously). Blend very well.
Pour the contents of the blender onto the chunks of beef heart and mix well. Cover with plastic wrap and marinate in the refrigerator for a minimum of 3 hours, or up to overnight.