Well, not actually. It's pink, but the blood that flows through it makes it appear to be red.
Everything seems to be red on Duolingo, the heart, the head, the neck, the legs, the feet, the arms. I think they have covered the whole body in the exercises.
I guess maybe Duo was referring to the lesson hearts.
Really difficult to hear "rot"... Would "ein Herz ist tot" as 'a heart is dead' be a valid sentence?
Yes, but the voice clearly says "rot".
One could listen...
"Ein Herz ist Brot"