The radial artery, which is located on the outer side of the forearm, can be used in interventional procedures, such as cardiac catheterization, to provide access to the arterial blood supply. In order to facilitate successful catheterization of the artery, a dilated artery and one free of arterial spasm is desirable. The proposed study will randomize twenty three healthy subjects to determine the effect of topical nitroglycerin on radial artery vasodilation. In the first phase of the study, which is a dose escalation study, each subject will receive either one or two inches of nitroglycerin in a blinded manner on one wrist and placebo on the other. Radial artery diameter will be measured with ultrasound at regular intervals up to two hours. The subjects will then return at a later date at which point they will receive the alternate dose on one wrist and placebo on the other. In the second phase of the study, we will randomize the same patients to a mixture of topical nitroglycerin and lidocaine or topical lidocaine alone. Measurements of radial artery diameter will be performed as in the first study.