This study evaluate the dosage of bisoprolol plasma residual concentrations in chronic heart failure with mild to reduced ejection fraction adult patients by dose and renal function.

The clinical relevance of bisoprolol plasma residual concentration in the management of HF medical therapy and the impact of renal function on reaching the maximum tolerated dose has never been studied. The investigators will perform an observational study to answer this issue.

In this study, there will be no changes of the doses of bisoprolol, whatever the bisoprolol plasma concentration, with the exception of vital threatening concentrations. This study is a pilot study.

Participants will be consecutive ambulatory chronic heart failure patients followed at the CHU de Caen, treated with maximum tolerated dose of bisoprolol with mild to reduced ejection fraction. Participants can benefit of the other heart failure recommended treatment at the exception of ivabradine that would confound the bisoprolol effect on heart rate. Participants will be subsequently studied by renal function.

Patients will be followed at one year with the electronic health record of the CHU de Caen for clinical events.

Inclusion Criteria:

• Consecutive ambulatory patients with chronic heart failure with mild to reduced ejection fraction (LVEF < 50%) at the CHU de Caen
• Aged 18 y.o. or older
• With a stable heart failure (see exclusion criteria)
• At the maximum tolerated dose of bisoprolol for at least one week (maximum dose reached without adverse tolerance event: orthostatic hypotension, symptomatic bradycardia, fatigue related to the treatment)

Exclusion Criteria:

• Unstable HF, that are patients who presented in the last 3 months before inclusion an hospitalization for any cardiovascular event including HF, new onset or worsening of HF or coronary artery disease symptoms
• Patient refusing to participate
• Patients with a non maximum tolerated dose of bisoprolol
• Patients with ivabradine intakes
• Body weight < 60kg or > 100kg
• Severe liver insufficiency
• Pregnancy
• Liberty deprived patients

Consecutive ambulatory chronic HFrEF patients followed at the CHU de Caen, treated with maximum tolerated dose of bisoprolol. Patients can benefit of other HFrEF recommended treatment at the exception of ivabradine that would confound the bisoprolol effect on heart rate. Patients will be subsequently studied by renal function (altered if creatinine clearance < 30mL/min, mild altered between 30-60mL/min, normal > 60mL/min as estimated by the CKD-EPI formula) and bisoprolol dose (5, 7.5 or 10mg).