Efficacy of Endothelin Receptor Antagonism in Coronary Artery Spasm

The goal of this randomized clinical trial is to assess if adjunctive bosentan therapy, in comparison to placebo, can reduce the rate of epicardial vasospasm at follow-up spasm provocation CFT (fuCFT) in patients with previously proven epicardial vasospasm on acetylcholine reactivity testing (at index CFT) and ongoing angina(-like) complaints. Participants will * Use either endothelin receptor antagonist or placebo for 10 weeks * Undergo follow-up acetylcholine spasm provocation test after 10 weeks * Answer online questionnaires on angina and quality of life