s correct that local anesthetics contain both
lidocaine and adrenalin (epinephrine). They both can have effects on the
heart, adrenalin has an obvious effect and lidocaine is actually an antiarrhythmic drug (class 1b sodium blocker) which may have proarrhythmic effects.
The problem is - adrenalin is added to prevent the lidocaine from having systemic effects, the blood vessels are constricted. If you have reactions towards lidocaine, choosing the one without adrenalin would be bad.