HMV (a leading music retail chain) are apparently advertising "Storyteller" as "containing the singles "Smoke Break" and "Heartbeat".
While it could be argued that this has jumped the gun, based on the fact that "Heartbeat" was pre-released and has done well on various sales charts - it does have the look of being official, as the two titles appear slowly in the promotional advertisement, one after the other, using the album type-face (and the other pre-releases are not mentioned)
Taking it at face value, therefore, it does look as if "Heartbeat" has probably been named as the second single in the UK. (That need not imply the US as well, since it is not that unusual to release different singles in different markets.)
We have no national radio network dedicated to Country Music, so singles are of less significance here - but if this does prove to be a release, they would be aiming to have it played in various slots on more general radio stations. BBC Radio 2 - an "Adult" Pop and General Music station - carries one well-listened weekly Country show - but also has a number of slots that concentrate on genre-free new and innovative music. It might be felt that "Heartbeat", which has some Country instrumentation, but an overall Pop-leaning feel, and a relatable romantic lyric, would fit well into that programming.
To me, it would not be the choice I'd hope for - primarily because I don't think it best represents stylistically what Carrie is doing on the stronger songs of this era. Also it strikes me as having a more "corporate" Mainstream style - and I don't see that as having a large impact here. If her team want a gentler song, I think it would probably do better later in the cycle (and I'd prefer it to be LINLYA, which strikes me as both more distinctive, and closer to what people here have liked on the "Nashvile" TV series.) But at this stage in the cycle, I think they might do better to hit hard with one of the dramatic songs.
"Church Bells" would be my top choice for second single. The Country shows here are mostly regional - but that needn't be a disadvantage. The national network could well play a hard-hitting song which is stylistically dramatic and interesting. Carrie's best chance, I feel, is to make her mark here as unique and different, rather than trying to "fit in" with a song that is considered internationally more neutral (a tactic that often risks losing much real impact)