Heaviness/pressure after eatin...Mostly on the upper central adbdomen...Other symp: fullness, pressure, discomfort...No pain. What could cause? "

Many possibilities. Acid reflux, peptic ulcer disease, & gall bladder or bile duct disease would top the list. Other causes: functional esophageal disorder, achalasia, non-ulcer dyspepsia, malignancy, and atypical presentation of coronary disease would be considered. You need evaluation and testing to get an accurate diagnosis leading to appropriate treatment.
Unstable angina. This can be your presentation of unstable angina -- meaning coronary heart disease as presented or induced by meals consumption and this is considered unstable -- please see your doctor asap.