Cavalier King Charles Spaniel vs Papillon

Heart disease isn't a risk for Cavaliers so much as a near-certainty — about half develop a heart murmur from mitral valve disease by age 5, and veterinary sources note that essentially every Cavalier that lives long enough will eventually develop it, making it the breed's leading cause of death.

Papillons are genuinely physically fragile — a toddler's rough handling, an accidental step, or a jump off the couch can cause a serious injury or broken bone, which is why many reputable breeders won't place puppies in homes with very young children.