Heinz tomato soup can be fattening if you eat too much of it.
But eating some Heinz tomato soup in moderation shouldn't be fattening and can be a good option when losing weight.
I lost weight while eating Heinz canned tomato soup so it certainly wasn't fattening when I ate it in moderation.
Each serving of Heinz tomato soup contains 59 calories so if you just watch your intake of it then it won't be fattening.
However if you're looking to fatten up and gain weight then if you do eat enough of the Heinz tomato soup then it certainly could eventually fatten you up.