A method of treating degenerative mitral valve disease (DMVD) in a companion animal having DMVD, a method of preventing DMVD in a companion animal at risk thereof, and a method of maintaining or improving cardiac health in a companion animal. The methods include orally administering to the companion animal a composition containing medium chain triglycerides and optionally one or more of omega-3 fatty acids, vitamin E, lysine, taurine, magnesium, or sulfur-containing amino acids.