Volume Challenge Added to DSE in the Diagnosis of Severe LFLGAS

Inclusion Criteria: * Age \> 18 years * Written informed consent * Patients with LFLGAS (mean Gradient: \< 40 mmHg, AVA ≤ 1.0 cm2 (by continuity equation using LVOT diameter) SVI ≤ 35 ml/m2), by rest TTE Exclusion Criteria: * Hypersensitivity to dobutamine or midazolam * Lack of safe contraception defined as: Female participants of childbearing potential not using and not willing to continue contraception for study duration, such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices. * Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc., * Enrolment of the investigator, his/her family members, employees and other dependent persons * Previous enrolment into the current study, ADDITIONAL SPECIFIC EXCLUSION CRITERIA REGARDING STRESS ECHOCARDIOGRAPHY: * Systolic left ventricular ejection fraction (LVEF) \< 20% * More than mild aortic regurgitation * Mitral valve disease, defined by mitral valve area \< 2.0 cm2 or more than mild mitral regurgitation * Unstable angina * Acute pulmonary oedema * Signs of relevant left ventricular heart failure defined as crackles more than one fourth of lung field on auscultation * Signs of relevant right ventricular heart failure defined as central venous pressure (CVP) \> 15 mmHg estimated with dilatation and collapsibility of vena cava inferior (VCI) * Severe pulmonary, renal or hepatic disease ADDITIONAL SPECIFIC EXCLUSION CRITERIA REGAR…