The goal of this clinical trial is to learn whether beta-blockers can improve coronary blood flow and reduce resistance in patients with angina and no obstructive coronary arteries (ANOCA). The main questions it aims to answer are: * Do beta-blockers improve coronary blood flow in patients with ANOCA? * Do beta-blockers reduce coronary microvascular resistance in these patients? Researchers will compare a beta-blocker to a placebo to see if the medication has measurable effects on coronary circulation. Participants will: * Receive a beta-blocker or a placebo * Undergo specialized heart tests (such as coronary flow and resistance measurements) before and after treatment.