Cavalier King Charles Spaniel vs Havanese

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.

Havanese are a genuinely sturdy, healthy toy breed by small-dog standards, but the silky coat is a real daily-brushing job, and this breed bonds so hard to its people that separation anxiety is a common, real problem, not an occasional quirk.