The purpose of the study is to measure how much nitroglycerin or its metabolites may be found in the bloodstream when MQX-503 or an FDA approved Nitroglycerin ointment 2% USP is applied to the skin of healthy subjects.

Inclusion Criteria:

• Healthy volunteers 18 - 70 years of age.
• Subjects able to give written informed consent and comply with study requirements.
• Subjects willing and able to safely discontinue all current prescription therapies.
• Subjects who will agree not to participate in other clinical trials.
• Negative pregnancy test in fertile females and agreement to use effective contraception throughout the study.

Exclusion Criteria:

• Persons who would be put at risk by discontinuing prescription therapies.
• Subjects with a known allergy to nitroglycerin.
• Subjects who have a condition or issue that would adversely affect the application of study medication, study evaluations or the subject's ability to comply with the protocol.
• Subjects who recently experienced myocardial infarction, uncontrolled congestive heart failure, unstable angina, uncontrolled hypotension or uncontrolled hypertension.
• Subjects who have participated in a study of an investigational drug within two weeks of visit 1.
• Subjects who have screening lab values that are out of range or are considered clinically significant by the investigator.
• Subjects who have had major abdominal, thoracic, or vascular surgery within 6 months of visit 1.
• Subjects with non-epithelialized skin lesions or interfering skin conditions at the time of screening in the area where study medication is to be applied.
• Pregnant or nursing women.
• Women of childbearing potential who are unwilling to comply with the contraceptive requirements.