What could cause random twitching in my chest, above the heart, possibly a vessel? No sob or pain.

More likely muscle. Muscle fibers 'twitch'. An artery carries blood from the heart to rest of body and pulsates rhythmically. Veins carry blood from the body back to the heart slightly bluish, but flatten easily. So you probably r having some random small muscles in the chest wall contracting, causing a twitch. Not likely serious. Often see with muscle fatigue. Weight lift? Sleeping poorly? Tired these days?
Could be muscles. Could be having twitcings in pectoral or intercoastal muscles.Get your potassium and magnesium checked.