Inclusion Criteria:

• Admitted to either an intensive care unit or progressive care unit with hemodynamic instability or decompensated/end-stage heart failure resulting from an acute medical problem (i.e. primary admission diagnosis is medical).
• Presence of cardiac pacemaker (including both temporary and permanent devices, as well as implantable defibrillators).
• Presence of any of the following invasive hemodynamic monitoring devices:
  • Pulmonary artery catheter
  • Arterial catheter
  • Central venous line (including peripherally-inserted central catheters)
• Stable blood pressure on current vasoactive medical therapy (if required), without need for fluid bolus or adjustment of vasoactive therapy for at least 1 hour.
• Resting heart rate < 100 bpm.
• Age > 18 years.

Exclusion Criteria:

• Inpatient surgery during this hospitalization as the reason for admission (i.e. primary admission diagnosis is surgical).
• Pacemaker lead or generator dysfunction, including lead fracture or need for battery change within 3 months.
• Pregnancy.
• Intra-aortic balloon pump or other percutaneous or surgical circulatory support, including Impella, TandemHeart, peripheral or central veno-arterial extracorporeal membranous oxygenation (ECMO).
• Hypertrophic Obstructive Cardiomyopathy (HOCM) with resting or inducible left ventricular outflow tract (LVOT) gradient.
• Amyloid cardiomyopathy.
• Severe mitral stenosis or severe aortic regurgitation.
• Not hemodynamically stable to participate in the study at the discretion of the treating physician.
• Recent (within 1 hour) need for vasoactive medication adjustment or fluid bolus to treat hemodynamic instability; once patients have stabilized from a hemodynamic standpoint, they may be reconsidered for study participation.
• Recent unstable arrhythmia or requiring intravenous antiarrhythmic drugs.
• Active/ongoing myocardial ischemia.

The data collected will include the following:

• Height and weight (body mass index [BMI]).
• Demographics, medical history, including cardiovascular history and results of previous testing.
• Medications (outpatient and inpatient).
• Vital signs.
• Pacemaker device and lead models.
• Pacemaker interrogation data.
• Hemodynamic measurements (see below).