Sobirin 2019.

Study characteristics
Methods	unblinded, randomised controlled clinical trial with parallel design
Participants	30 participants with clinical heart failure were randomised. Inclusion criteria: age ≥ 45 years, NYHA functional status II to IV, EF ≥ 50%, evidence of diastolic dysfunction on non‐invasive imaging, and who had received standard heart failure treatment for 4 weeks before the study Exclusion criteria: chronic atrial fibrillation, acute coronary syndrome or coronary revascularisation within 60 days, clinically significant valvular disease, significantly low systolic blood pressure (< 100 mmHg) or high blood pressure, people with a prior LVEF < 40%, known infiltrative cardiomyopathy (e.g. amyloidosis), hypertrophic cardiomyopathy or chronic pericardial disease, dyspnoea or oedema due to non‐cardiac causes, such as pulmonary disease, and anaemia (Hb < 8.0 g/dL), inability or refusal to provide informed consent, poor echocardiographic recordings 15 participants were randomised to coenzyme Q10 group and 15 participants to the control group
Interventions	Intervention with dose: oral coenzyme Q10 100 mg three times a day + conventional therapy Control: conventional therapy alone
Outcomes	Outcomes measured at 30 days Used in this review: left ventricular ejection fraction measured by echocardiography Not used in this review (not outcomes of interest): parameters for diastolic function (E/e' ratio, medial and lateral e', E velocity, E/A velocity ratio, deceleration t and LAVI), diastolic and systolic left ventricle internal diameter. left ventricular mass index
Notes	1 participant in the treatment group and 1 participant in the control group were lost to follow‐up, and were excluded from the analysis
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	study is randomised; randomisation done by permuted blocks with a ratio of 1:1
Allocation concealment (selection bias)	Unclear risk	Details about allocation concealment were not mentioned
Blinding of participants and personnel (performance bias) All outcomes	High risk	Study was unblinded
Blinding of outcome assessment (detection bias) All outcomes	High risk	Study was unblinded
Incomplete outcome data (attrition bias) All outcomes	High risk	Of the randomised participants, 2 participants were not included in the analysis
Selective reporting (reporting bias)	High risk	Some outcomes listed in the protocol were not reported in the manuscript (plasma malondialdehyde level, quality of life was measured using the Minnesota Living with Heart Failure Questionnaire (MLHFQ))
Other bias	Low risk	No other risk of bias was found