Even half of patients with angina undergoing invasive coronary angiography presents without any significant epicardial stenosis. In these cases, symptoms are usually caused by coronary microvascular dysfunction (CMD), developing as a result of several potential underlying pathophysiologies. A wide range of underlying pathomechanisms makes it challenging to develop molecular-targeted pharmacological solutions; thus, direct physiology modification has been introduced as a promising concept. The coronary sinus reducer (CSR) narrows the coronary sinus, which causes symptom relief in patients with refractory angina and coronary stenosis. CSR implantation aims to increase the coronary sinus pressure, which raises venous back pressure into the myocardium. Despite several hypotheses, the exact physiological mechanisms remain not fully elucidated. Recent data from observational studies also suggest the beneficial effect of CMD on microvascular indices. To date, there are limited data regarding the efficacy of this solution in patients with angina with no obstructive coronary artery disease (ANOCA). Of note, patients with ANOCA are frequently burdened with other comorbidities, such as heart failure with preserved ejection fraction (HFpEF). HFpEF presence relates to worse prognosis and higher risk of future cardiovascular events. Previous works showed that HFpEF is significantly associated with the appearance of CMD. Due to the small variety of drugs for HFpEF, treatment targeting CMD may be a promising therapeutic target for this disease. To date, there is also no data regarding the impact of CSR implantation on function of left ventricle and echocardiographic indexes impaired in diastolic dysfunction in patients with ANOCA. Proposed study aims to evaluate the CSR as a therapeutic strategy in patients with ANOCA to improve angina, as well as quality of life and will deliver the results regarding CSR impact on diastolic function of left and right ventricle. This study will also evaluate the mechanisms standing behind the benefits of CSR use. Neovasc reducer produced by Shockwave Medical inc will be used as CSR device in this study. Proposed study may lead to the introduction of the Neovasc reducer to the guidelines for ANOCA patients. It will also provide the data on Neovasc reducer potential use as a supportive therapy in patients with HFpEF. Prospective, single-arm cohort study including patients with angina with no obstructive coronary artery disease. Enrolled patients will undergo the Neovasc reducer implantation with periprocedural evaluation of coronary microcirculation before and directly after the device implantation. All patients will be assessed with echocardiography (evaluation by external corelab) at baseline and at six months of follow-up. Patients will also undergo exercise testing (six-minute walk test) and assessment of quality of life (SF-36), as well as angina severity (Seattle Angina Questionnaire, Dedicated app and Canadian Cardiovascular Society grade).