Below is Manuela Color 213 size 20, not too bad of a thread and added it to the order as an afterthought. This is Hearts Desire by Susan K. Fuller and I have done it a few times before.
I did see a knot as I was winding my shuttle and ran into some slight unevenness in the thread so I adjusted my tension so it did not cause any issues.
The pattern for this heart can be found on Le Blog de Frivole on the patterns page.