Inclusion Criteria:  Beta-blockers naïve patients Patients been on beta-blocker therapy for at least 4 weeks. Age (18-75) Years old.  Exclusion Criteria:  Non-Egyptians. Kidney failure of any stage. Liver failure of any stage. Malignancy. Pregnancy. HR < 55 beats/min (in the absence of b-blocker therapy). Presence of a cardiac pacemaker.