I know I have an inverted uterus; they spotted this at my 8-9w scan. But later scans no-one noticed; you can't once the uterus starts growing. Maybe this was the case wtih you? A big baby-filled uterus is all out of shape and the "normal" shape wasn't recognisable?

I would think that it would be quite hard to diagnose an oddly-shaped uterus from a section, tbh, because it's so big and stretched. Maybe you need to have an ultrasound when it's back to "normal" to confirm this diagnosis?

And it's safer to wait a bit between babies when you have sections; give the wound time to heal before you stretch it out again IYSWIM.

Hope you get some answers, maybe ask/write to the doctor who told you that you had a heart-shaped uterus why he feels that and what it actually means for you.

Best of luck!