Efficacy Study of Oral Nicorandil on Improving Microvascular Function in Female Non-obstructive Coronary Artery Disease (CAD) Participants

Inclusion criteria: * Female * Participants aged 18-70 years * Participants with typical stable angina but without coronary obstruction (defined as coronary occlusion less than (\<) 50%) by invasive coronary angiography or coronary computed tomography angiography (CTA) in recent three months * All other long acting cardiovascular disease medicines, including but not limited to aspirin/clopidogrel, calcium channel blockers (CCB), Angiotensin-converting enzyme inhibitors (ACEI)/Angiotensin II Receptor Blockers (ARB), beta-blockers, statins, ivabradine, trimetazidine, et al, should be stable taken for at least two weeks before screening period * For participants who met these four criteria above, MFR will be tested by stress PET. Participants whose MFR \<3.0 could be included in the study Exclusion criteria: * Severe or uncontrolled hypertension (resting Systolic blood pressure \[SBP\] \>=160 millimeter of mercury (mmHg), or resting Diastolic blood pressure \[DBP\] \>=100mmHg at screening period) * Participants with shock (including cardiogenic shock), or hypovolemia * Severe hypotension (resting SBP\<90mmHg，or resting DBP\<60mmHg) * Significant valvular heart disease, congenital heart disease or cardiomyopathy * Congestive heart failure(New York Heart Association \[NYHA\] III-IV), echocardiographic ejection fraction\<45% * Acute pulmonary edema; * Hepatic or renal dysfunction, defined as: * Serum Alanine Aminotransferase (ALT) \> triple of the normal value upper limit; * Serum Aspartate Aminotransferase (AST) \> triple of the normal value upper limit * Serum creatinine \> twice of the normal value upper limit * Glaucoma * Active peptic ulcer or active skin ulcer * Taking glyburide, phosphodiesterase type 5 (PDE-5) inhibitor, soluble guanylate cyclase stimulator(s) * Known to be hypersensitivity to nicorandil, nitrates, niacin, or any of the excipient * With contraindication to complete stress PET test * No legal ability and legal ability is limited * Participants unlikely to cooperate in the study or with inability or unwillingness to give informed consent * Child-bearing period women without effective contraceptive measures, pregnancy and lactation * Participation in another clinical trial within the past 30 days * Other significant disease that in the Investigator's opinion would exclude the participant from the trial