Biogirl,
These are quite different drugs. Among the BP meds the calcium channel blockes have probably the largest differences among them.
Norvasc is amlodipine and Cartia is diltiazem.
You may do very differently on one or the other. Stay with the one that has the best combination of price, results, and side effects for you. Since the Norvasc is NOT available generically, it's at least twice as expensive as diltiazem.