If you could go back in time and observe the first heart, what would you put in your notes? Would it be in a prehistoric dinosaur or a monkey, or a human? In all three, it does the same thing.
When did it arrive? It couldn’t appear by itself or will itself into existence nor slowly build itself into its purpose.
The purpose of the heart is to pump blood thru veins and arteries to supply life-giving nutrients and oxygen from the lungs for the entire body. For the heart to survive, it needs electrical currents to make it do its job.
The heart would be useless and dead if all of the above and more were not present simultaneously. This applies to all life. This has been termed irreducible complexity. It makes sense.
This is why I know with absolute certainty there is a Creator God. To think all this happened by blind unthinking chance slowly over millions of years requires faith greater than a belief in an intelligent Creator.
Therefore, I lack faith in being an evolutionist, atheist, or evolutionist theist.
The first heart likely looked much like it does it now. It was in the body of Adam, Eve, and the animals God created the 1st week of planet Earth. All were fully functional the moment God spoke it.
“I will praise You, for I am fearfully and wonderfully made; Marvelous are Your works, And that my soul knows very well.” Psalm 139:14