What comprises a cardiac episode, other than an arrythmia?

I'm 53, postmenopausal, and a widow of a 2 pk/day smoker. 5'2"/122. Fairly active (walk everywhere), nonsmoker/nondrinker. I do oatmeal 3x week, and eat salads for lunch. Blood work showed slightly elevated Triglycerides (I love brownies) and bad cholesterol was really low; good 2.5 x normal. I've been on a heart monitor for 2 weeks because I have been ping out. I feel a "flutter" and hit the ground. I've had an echo, EKG, nuclear stress tests done. Any ideas?