The purpose of this research study is to learn about the effects of a medication called Vyvanse on the heart (cardiovascular system). The U.S. Food and Drug Administration (FDA) has approved Vyvanse for the treatment of Attention Deficit Hyperactivity Disorder (ADHD). People who have ADHD have trouble paying attention, organizing, and planning; these symptoms can cause problems at work, socially and at home.

Vyvanse (also known as Lisdexamfetamine) is a stimulant class medication. There have been reports of serious cardiovascular effects in children and adults treated with stimulants. While there is no definite evidence that these events were related to the use of stimulants, the deaths have raised questions about the cardiovascular safety of stimulants.

The study will involve in-depth cardiovascular tests, namely echocardiograph (ultrasound of the heart) and cardiopulmonary exercise test (also called stress test; subjects exercise on a bicycle while measuring their heart activity and breathing is monitored by cardiologists).

The investigators predict to see changes in blood pressure and heart rate as shown in previous clinical studies, and that the in-depth cardiovascular tests will provide new insights into the cardiovascular impact of stimulants.

Inclusion Criteria:

1. Male and female outpatients 18-60 years of age.
2. A current DSM-IV-TR diagnosis of ADHD, confirmed by the Adult ADHD Clinical Diagnostic Scale (ACDS) at Screening.
3. In phase two only; Stage I primary hypertension (SBP 140-159 mm Hg/DBP 90-99 mm Hg) as defined by Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (Chobanian et al, 2003).
4. In phase two only; Treatment with stable doses of up to two FDA approved antihypertensive medications achieving a stable blood pressure of <135/85. Acceptable classes of medications include diuretics, beta-blockers, angiotensin-converting-enzyme (ACE) inhibitors or receptor blockers, aldosterone antagonists, calcium-channel blockers (Rosendorff et al, 2007).

Exclusion Criteria:

1. Pregnant or nursing females.
2. Clinically significant cardiovascular history, including angina, syncope, thrombosis, aneurysm, myocardial infarction, myocarditis, valvular disease, heart failure, or arrhythmia. Hypertension is exclusionary in phase one subjects.
3. In phase two; hypertension is not exclusionary, however blood pressure with antihypertensive treatment of ≥135/85 at baseline is exclusionary.
4. Clinically significant or unstable medical condition including pulmonary (asthma, edema, thrombosis), renal, hepatic, metabolic (thyroid) or neurological disorder, based upon a medical history.
5. Orthopedic impairment or BMI that significantly impacts or restricts exercise performance testing, per clinician judgment.
6. Any clinically unstable psychiatric conditions including suicidality, homicidality, bipolar disorder, psychosis.
7. Current (within 3 months) DSM-IV-TR criteria for current abuse or dependence with any psychoactive substance other than nicotine, including alcohol, prescription medicines and/or street drugs. In addition, subjects with clinically significant histories of dependence on alcohol, prescription medications or "street drugs" will be excluded, if such history places subjects at heightened risk, and/or may be associated with cardiovascular sequelae, based on clinician judgment.
8. Ongoing treatment with any psychotropic medication, including anxiolytics, antidepressants, mood stabilizers.
9. Use of Monoamine Oxidase Inhibitors (MAOIs) including linezolid within two weeks prior to starting study medication.
10. Mental retardation (IQ < 75).
11. History of intolerance or allergy to LDX.
12. Diagnosis of glaucoma