Evaluation of a New Non-Invasive Device for Detection of Endothelial Dysfunction

Inclusion Criteria: 1. Male or female between the ages of 18-65. 2. Ambulatory 3. FMD ultrasound assessment within past 6 months. 4. No clinical evidence of cardiovascular disease (no history of MI, TIA or stroke, limp, carotid or aortic murmurs) 5. 10 hour fast - water only 6. Normal peripheral pulse examination. 7. ECG without evidence of former MI or LVH. 8. Capable of understanding the explanation and signing informed consent. Exclusion Criteria: 1. Below age 18 and above age 65. 2. Pregnancy 3. Has not had FMD ultrasound assessment within past 6 months. 4. Exhibits clinical evidence of cardiovascular disease (history of MI, TIA or stroke, limp, carotid or aortic murmurs, clotting disorder) 5. Has eaten or drunk anything besides water in past 10 hours. 6. Known sensitivity to NTG 7. Takes medication for asthma, heart disease or depression, such as atenolol (Tenormin); carteolol (Cartrol); labetalol (Normodyne,Trandate); metoprolol (Lopressor); nadolol (Corgard); phenelzine (Nardil); propranolol (Inderal); sotalol (Betapace); theophylline (Theo-Dur); timolol (Blocadren); tranylcypromine (Parnate), and tricyclic antidepressants such as Elavil 8. Anemia, glaucoma, or have taken medication such as calcium channel blockers like amlodipine (Norvasc), diltiazem(Cardizem), felodipine (Plendil), isradipine (DynaCirc), nifedipine (Procardia), and verapamil (Calan, Isoptin); dihydroergotamine (D.H.E. 45) 9. Venopuncture of arms within past week 10. Use of Viagra, Levitra, Cialis or similar medications to treat erectile dysfunction within last 24 hours or planned use within 8 hours 11. Any of the following: * unstable emotionally * unable to understand explanation of study * ECG with evidence of former MI or LVH. * Abnormal peripheral pulses 12. Has not signed an informed consent form. 13. Patient is enrolled in another clinical study.