When I began to read I thought you were going to say heart murmur so I'm happy it's just weight.
I wouldn't worry. Soleil looks a lot like Gus was and he was very healthy. Just a great metabolism and a lot of energy. My one vet made a comment when he was a year and a half (took him that long to fill out) how she was glad to see him finally at a healthy weight. He'd been healthy all along, just naturally thin. Almost made me feel like she thought
I was keeping him skinny.
She looks great!!