Inclusion Criteria:

• * Men and women older than 18 years
• * Established diagnosis of heart failure with preserved ejection fraction (HFpEF) including left ventricular ejection fraction (LVEF) ≥50% as evidenced by Doppler echocardiography and/or ratio of the early mitral inflow velocity (E) to septal tissue Doppler velocity (e') \>8 and at least 1 other sign of chronically elevated filling pressures, including an enlarged left atrium (left atrial volume index \>34 mL/m2), an elevated N-terminal pro-brain natriuretic peptide (NT-pro-BNP) level within the past year, long-term loop diuretic use for control of symptoms, or elevated filling pressures (mean pulmonary capillary wedge pressure \>12 mmHg) on prior cardiac catheterization
• * Stable medical treatment

Exclusion Criteria:

• * Recent hospitalization (within the previous 1 month)
• * Unstable angina and/or uncontrolled cardiac arrhythmia causing symptoms or hemodynamic compromise (including severe bradycardia or tachycardia, sick sinus syndrome, or multifocal premature ventricular contractions)
• * Presence of any clinical condition that makes the patient unsuitable to participate in the trial, e.g., significant ischemic or valvular heart disease, cor pulmonale, unstable coronary artery disease, primary renal (e.g., estimated glomerular filtration rate (eGFR) \<25 mL/min/1.73 m2) or hepatic disease (e.g., aspartate aminotransferase and alanine aminotransferase levels \>3.0 times the upper limit of the normal range), pulmonary, neuromuscular, orthopedic disorders, among others
• * Inability to exercise on the treadmill
• * Inability to provide informed consent
• * Concern for inability of the patient to comply with study procedures and/or follow up (e.g., alcohol or drug abuse)
• * Any contraindication to heat therapy and/or inability to fit into water-circulating trousers
• * Impaired thermal sensation in the leg