Background: Landiolol, a highly cardioselective agent with a short half-life (2.4–4 min), is commonly used as a perfusor or bolus application to treat tachycardic arrhythmia. Some small studies suggest that prior oral β-blocker use results in a less effective response to intravenous β-blockers. Methods: This study investigated whether prior chronic oral β-blocker (Lβ) or no prior chronic oral β-blocker (L–) intake influences the response to intravenous push-dose Landiolol in intensive care patients with acute tachycardic arrhythmia. Results: The effects in 30 patients (67 55–72 years) were analyzed, 10 (33.3%) with and 20 (66.7%) without prior oral β-blocker therapy. Arrhythmias were diagnosed as tachycardic atrial fibrillation in 14 patients and regular, non-fluid-dependent, supraventricular tachycardia in 16 cases. Successful heart rate control (Lβ 4 vs. L– 7, p = 1.00) and rhythm control (Lβ 3 vs. L– 6, p = 1.00) did not significantly differ between the two groups. Both groups showed a significant decrease in heart rate when comparing before and after the bolus administration, without significant differences between the two groups (Lβ −26/min vs. L– −33/min, p = 0.528). Oral β-blocker therapy also did not influence the change in mean arterial blood pressure after Landiolol bolus administration (Lβ −5 mmHg vs. L– −4 mmHg, p = 0.761). Conclusions: A prior chronic intake of β-blockers neither affected the effectiveness of push-dose Landiolol in heart rate or rhythm control nor impacted the difference in heart rate or mean arterial blood pressure before and after the Landiolol boli.