How soon would a miscarriage happen if the heartbeat never started or stopped?

Its normal to not be checked until 10 to 15 weeks along because the baby is so tiny (like the tip of an eraser). Yes you would mc if the preg isn't viable and the heart stops. Most likely right now you wouldn't hear the heartbeat, at 10 weeks they told me they might not find the hb because of how tiny the baby is. No worrys, as long as your not bleeding everything is fine!