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 in 2 visits to determine the effect of topical nitroglycerin on radial artery vasodilation. Radial artery diameter will be measured with ultrasound at regular intervals up to two hours.

During the first study visit, as a dose-optimizing study, each subject will be randomly assigned to one of two Dose-Test arms to receive either 15mg or 30mg of nitroglycerin on one wrist and placebo on the other. Radial artery diameter will be measured with ultrasound at regular intervals up to two hours. On the second study visit, the same participants will be randomly assigned to one of two Combination-Test arms to receive bilateral topical application of either 20mg or 40mg of lidocaine; the lidocaine will be applied in combination with 30mg of nitroglycerin on one wrist and in combination with placebo on the other wrist. Measurements of radial artery diameter will be performed as in the first visit.

Inclusion Criteria:

• Willing and able to give written informed consent and comply with study requirements
• Patient who speak English

Exclusion Criteria:

• Presence or history of liver, cardiovascular, rheumatologic, cancer or renal disease.
• Current treatment with any vasodilator therapy
• Systolic blood pressure of less than 90 mmHg
• History of radial artery catheterization within the previous year
• Absence of radial artery blood flow in one or both arms
• Pregnancy.
• Active infection
• Staff members of the Cardiac Catheterization Laboratory.