So... could this be a treatment for enlarged hearts?

Interesting!

People do no realize how wide spread the GLP1 receptors are in the human body. GLPL1R is expressed on all muscles so heart muscle will be effected:

https://pmc.ncbi.nlm.nih.gov/articles/PMC5939638/

https://www.proteinatlas.org/ENSG00000112164-GLP1R/tissue

The way these drugs help loose weight is by increasing cellular activity by stimulating adenylyl cyclase and increased intracellular cAMP levels. It is not that hard and not a msytery to anyone who can think straight about human metabolism.