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.