system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do our hearts and lungs not get tired?

I presume it's something to do with their proximity to a fresh oxygen supply and that the toxins such as lactic acid would be pumped away quickly, but even then how do our hearts beat 24/7 without giving out?!
gpt
Our heart and muscles like the diaphragm that controls the lungs do simply have an incredibly rich oxygen supply. They don't generate lactic acid - lactic acid is what the body produces when there is a shortage of oxygen to muscles that require energy, so they revert from the much more efficient aerobic respiration to the lactic acid producing anaerobic respiration. The body provides these organs with enough oxygen so as to allow for aerobic respiration to continue.