Free fatty acids. Dr Eric Westman is one of the doctors I follow and have had the chance to meet personally, hear him speak at a conference and think very highly of what he says and has to offer. He is very science based and wants to see the data. He has headed a weight loss clinic at Duke University for I think around 20 years now.

Just after minute 7:12 is a chart that shows the utilization of energy by the heart. The entire presentation is 12 minutes long.
The heart muscle uses very little glucose for energy. It mostly runs on fatty acids. This is not commonly known but is fact.

Sorry! That was the wrong link I provided. Here is the correct link.
https://www.youtube.com/watch?v=DZhPpzXX0xo       #mce_temp_url#

Bonus link.
https://www.youtube.com/shorts/9dcuiGVHhSo       #mce_temp_url#