Running is definitely not for everyone; for some people, it's hard on their joints, and it does tend to cause injuries if it is not approached properly. Walking on a soft track, trail, or treadmill is also a good choice.
However, running or other intense aerobic activity may actually help people with heart palpitations. Increasing the heart rate affects electrical conductivity, and sometimes can sort of "re-set" the heart. I remember when I was having a particularly nasty bout of PVCs (pre-ventricular contractions) in college - several hundred over the course of a few hours - the on-call physician I contacted told me to take a brisk run around the block a couple of times. It was uncomfortable at first, but the palpitations vanished when I got my heart rate up to a solid 160 or so. However, people need to make sure that their palpitations are benign before they start slamming themselves with the intense aerobics :)