Before the reader jumps to any conclusion based upon the inclusion of the words gold and silver, let me make it clear that Pokemon Heart Gold and Soul Silver are updated versions of the 199 videogame Pokemon Gold and Pokemon Silver. These were role playing video games meant to be played on Nintendo DS. The latest version of Heart Gold and Soul Silver were published in 2009. Though the basic purpose in both the versions is to become a master trainer of all types of Pokemon’s, it is seen that there is a difference in settings as well as pokemon’s available in the game. This is achieved by defeating all other trainers in the game. Both Heart Gold and Soul silver take place in a fictional Universe where these creatures called Pokemon exist. These creatures have special abilities, and each variety has different ability than others.
The differences between Heart Gold and Soul Silver are subtle to say the least, and basically limited to the look and powers of the Pokemon you are likely to encounter inside the game. These types of Pokemon found in heart Gold before national Dex are Spinarak, Ariados, Growlithe, Mankey, Primeape, Mantine, Gligar, Phanpy, and Donphan. Corresponding Pokemon before National Dex in Soul Silver are Ledyba, Ledian, Vulpix, Ninetales, Meowth, Persian, Delibard, Skarmory, Teddiursa, and Ursaring.
Pokemon encountered after National Dex in Heart Gold are Sableye, Baltoy, Claydol, Latias, Kyogore, Mantyke, and Gliscor, while corresponding Pokemon after Natinaol Dex in Soul Silver are Mawile, Gulpin, Swalot, Latios, and Groudon.
One notable difference is in Pokemon that are not exclusive but are easier to obtain. Such Pokemon in Hear Gold are Caterpie, Metapod, Butterfree, Sandshrew, Sandslash and Ho-oh, while in Soul Silver these Pokemon are Weedie, Kakuna, Beedril, Ekans, Arbok, and Luiga.
Besides the difference in the Pokemon listed above , all other differences in Heart Gold and Soul silver are superficial and really do not matter much.