Heart disease is increasingly common in dogs - probably because their average life expectancy is increasing due to improved veterinary care. Some heart defects, eg hole in the heart, are present from birth (congenital heart defects) but only cause signs as the dog gets older. Other diseases develop later in life as a result of the effects of ageing or damage to the heart. The most common heart diseases in the dog develop as the dog ages and its heart starts to wear out.