Cavalier King Charles Spaniel vs Pug

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.

Pugs cannot breathe like a normal dog, and in the largest UK vet-record study of the breed they were found about 54 times more likely to be diagnosed with obstructed breathing than other dogs, on top of being far more prone to eye ulcers and obesity.