The goal of this double blind, outcome-assessor blind, randomized controlled trial, is to compare the effectiveness of external encounter counterpulsation (EECP) versus sham procedure in participants with long COVID-19 fatigue.

The main question[s] it aims to answer are:

• Whether EECP improves fatigue score
• Whether EECP improves quality of life, six-minute walk test, and endothelial function Participants will attend 15 sessions (1-hour each) of EECP during 5 weeks Researchers will compare EECP versus sham procedure for the above outcomes.

Participants of this trial will be patients recovering from acute COVID-19, 3-12 months following the acute infection, and suffering from fatigue with a Patient-Reported Outcomes Measurement System (PROMIS)-Fatigue short-form (SF)-7a score of > 50.

Exclusion criteria will include contra-indications for EECP (see protocl). Intervention, comparisn and outcomes are described above. Study plan: participants will be invited using social media, after filling a fatigue score (PROMIS) to test for eligibility. Those with a score of > 50 will be invited for a study visit.

Study visit 1 will include informed consent, followed by physician interview, physical examination, ECG; and will be referred for completion of blood tests including complete blood count (CBC) to rule out significant anemia (Hb< 12 for men or hb <10 for women) and serum beta human chorionic gonadotrophin (bHCG).

Eligible patients will then be randomized into two groups for treatment with EECP vs sham procedure. In study Visit 2 they will answer several questionnaires, perforn EndoPAT test to assess endothelial dysfunction, and six-minute walk test, followed by either:

1. Treatment group- 1 hour EECP session
2. Sham group - 1 hour of a sham EECP session (patients will be hooked to the EECP device but it will be set to the lowest setting, and lowest frequency, therefore unable to create a sufficient rise in diastolic return). This visit will be followed by 3 times weekly 1 hour sessions for 5 weeks (15 sessions) of either EECP or sham procdeure, according to randomization group.

Questionnaire that will be used before and after the intervention will include:

1. Fatigue evaluation using the PROMIS 7a form, attached in appendix (as validated on Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)patients)
2. Functional capacity evaluation using the Duke Activity Status Assessment (DASI) (https://www.mdcalc.com/duke-activity-status-index-dasi);
3. Shortness of Breath using the modified Medical Research Council dyspnea scale
4. Quality of life using the SF-36 questionnaire. 6mwt and endothelial dysfunction by EndoPAT will be held following the last treatment.

Study Visit 3 (3 months following starting treatment) will be a final Interview to assess improvement by questionnaires, as well as time to return to activity and time to return to work.

Inclusion Criteria:

• Patients recovering from PCR or lateral flow testing proven acute COVID-19
• 3-12 months following the acute infection
• Suffering from fatigue with a PROMIS-SF-7a T-score of > 50

Exclusion Criteria:

• Acute decompensated heart failure
• Recent myocardial infarction within the last 3 months
• Unstable angina pectoris
• Severe hypertension > 180/110 mm Hg
• Coagulopathy with international normalized ratio of prothrombin time > 2.0
• Moderate to severe aortic regurgitation
• Abdominal aortic aneurysm (>5 mm) or dissection
• Arrhythmias that may interfere with triggering of EECP system (uncontrolled atrial fibrillation, flutter and very frequent premature ventricular contractions)
• Heart rate of <35 or >125 beats per minute
• Any surgical intervention within 6 weeks before EECP
• Recent cardiac catheterization (1-2 weeks) or arterial femoral puncture
• Severe peripheral arterial disease
• Severe venous disease (thrombophlebitis, prior or current deep vein thrombosis or pulmonary embolism)
• Severe chronic obstructive pulmonary disease
• Pregnancy or women of childbearing age who do not have a negative pregnancy test

Data will be shared by approaching the PI, with reasonable request

Masking of participants - the sham procedure includes the same location of pneumatic blood-pressure cuffs used for the intervention; and will be perfoemd in the same frequency and duration as the intervention. Participants will be invited for the procedures at separate times to avoid connection between them.

Masking of investigator and outcome assessor - unblinded nurses and one unblinded physician will be responsible for performing the procedures (either intervention or sham), without involving other team members (other investigators or outcome assessors), who would remain blinded to the treatment arm.