InterventiOn of Biventricular Pacemaker Function on ventrIcular Function Among Patients With LVAD's

15 patients with advanced heart failure (HF) who have already undergone implantation of a continuous-flow left ventricular assist device (CF-LVAD) implantation. Inclusion criteria: 1. Have already received CF-LVADs and are clinically stable, 2. Ambulatory outpatients and are fully recovered (at least 3 months) from LVAD implantation; Exclusion criteria: 1. Individuals with clinical right ventricular (RV) failure under resting conditions, defined as moderate-severely reduced RV systolic function on echocardiography, or 2. Clinical evidence of RV failure (elevated jugular venous pressures, 3 or 4+ \[significant\] peripheral edema); 3. Disorders that adversely influence exercise ability (e.g. arthritis, peripheral vascular disease, pulmonary disease); and 10 healthy individuals will serve as a control group to define normal RV function during exercise. Inclusion criteria: 1\) Persons without a past medical history of cardiovascular disease or related disease such as: 1. hypertension, 2. diabetes, 3. peripheral vascular disease, 4. arrhythmias, f. are not taking any cardiac-related medications (e.g. antihypertensive medications). Exclusion criteria: 1. Individuals requiring systemic anticoagulation with vitamin-K antagonists or new/direct oral anticoagulants ("NOAC"/"DOAC"); 2. Disorders that adversely influence exercise ability (e.g. arthritis, peripheral vascular disease).