Inclusion criteria:  Age > 18 years. Patients admitted to ICU with septic shock.  Exclusion criteria:  Patients contraindicated to begin oral feeding (NPO patients). Patients diagnosed with arrhythmia. Patients taking drugs with known or suspected interactions with ivabradine (strong CYP3A4 inhibitors and QT-prolonging agents) within five half-lives prior to inclusion and during the first 24 h of the study.