Heart disease is a very common problem for people for are overweight, and especially for people who are obese. It is also a problem that is very near and dear to me, as my father died several years ago from a heart attack (even though he was in relatively good shape).
Some things you can do to help yourself get in shape are:
... Basically anything that will help you break a sweat is good for the heart. It's a muscle and if not used it won't work. Look at people in wheelchairs. In many cases if nervous activity was restored to their legs the legs would still not function because the muscle hasn't been used in such a long time.
This is why we need to exercise our hearts (even if you are skinny). Heart disease can strike anyone but it is certainly more prevalent in people who are overweight (75% more likley).