Could you move them around so the hearts in a row are the same height? If they're still uneven on row widths, add some of the checkered fabric to each end of the row and resquare. You might even offset the heart blocks so it won't be obvious the blocks are a little different in width. They're very pretty. And I love the bright colors against the black and white. Good luck! (0:

Thanks BJ great idea on off setting the blocks :)

Yes....add a sashing between the blocks. It could be narrow.

The hearts are so close to matching I think it won't be obvious w/ the sashing. Using the block fabric as a sashing would be problematic if you want to match the pattern in the fabric though.

I would also play w/ the block layout so the ones next to each other come as close to matching as you can manage.
Place the best matching blocks to the center and poorest matching to the outer sides or bottom. (away from the main focus)

If you add a sashing then each heart will be a stand-alone block, rather than part of a row. The matching won't be an issue because there will be enough distance between the hearts and the eye won't read it as a mismatch.

Here is a quick idea of both black and check narrow sashing. Not precise just to give an idea

I don't think it will. You can do some easing in and it will help. Just my opinion and I'm no expert.

I think you could ease/stretch the blocks to match. As I hear said on Fons and Porter - "baggy {on the} bottom" when you sew the blocks together. The feed dogs will help ease the little bit in.

My concern w/ sashing is that if it is narrow sashing, if it isn't exactly perfect, that will be noticed, too.

I love your colors and esp the black and white!!

I agree with a narrow sashing. Probably you will be the only one to notice it once it is finished.