The primary reason the investigators are doing this study are to understand how the right side of the heart functions in heart failure patients with left ventricular assist devices (LVADs, or "mechanical hearts"). Second, the investigators are interested in understanding how different pacemaker settings influence function of the heart at rest and activity.

Healthy individuals, as well as patients with advanced heart failure supported by LVADs, completed invasive hemodynamic analysis at rest and with exercise to characterize right-sided heart function at rest and with exercise during invasive cardiopulmonary exercise testing on upright cycle ergometry.

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).

15 patients with advanced HF who have already undergone CF-LVAD implantation.

10 healthy individuals will serve as a control group to define normal RV function during exercise.

Healthy individuals are those who are free of cardiovascular disease and not on any medications to treat a cardiovascular disease. Patients with LVADs are those with a history of advanced heart failure who are supported by an LVAD

8 Weeks