You are my heat!

It was Marc's birthday and I wanted to write something profound in his little birthday card.
I had bought him a kind of bubble spa thing for his poor feet that often hurt in the evenings.
I wrapped it up and prepared a nice card deliberately avoiding the urge to be funny, no jokes and no sarcasm.
Since I sometimes (?) razz him about his homely toes and purple ankles, I figured it was time to just be nice and let him know I love him.
I told him I loved all of him, including his feet.
I told him he was my heart and my life, I thought.
When he opened the card, he seemed puzzled.
He held it this way and that way, trying to decipher the message.
Exasperated, I reached over and took the card.
"See, it says "You are my rack? rust? rook? and my hert? hees? hunt?" I tried to tell him.
But I couldn't read my writing either.
I'm obviously been a journalist too long. I write like a doctor.
I huffed off.
Several days later, I picked the card up and studied the message.
What could I have meant to say?
Finally, the mist cleared: "You are my rock and my heart!"
Of course, clear as a bell.
There you have it.
Much better than "You are my rust and my heat, "don't cha think?
What's hard to understand about that?