Voltage-gated L-type Ca²⁺ channels (LTCCs) containing a pore-forming α1D subunit (D-LTCCs) are expressed in neurons and neuroendocrine cells. Their relative contribution to total L-type Ca²⁺ currents and their physiological role and significance as a drug target remain unknown. Therefore, we generated D-LTCC deficient mice (α1D^−/−) that were viable with no major disturbances of glucose metabolism. α1D^−/− mice were deaf due to the complete absence of L-type currents in cochlear inner hair cells and degeneration of outer and inner hair cells. In wild-type controls, D-LTCC-mediated currents showed low activation thresholds and slow inactivation kinetics. Electrocardiogram recordings revealed sinoatrial node dysfunction (bradycardia and arrhythmia) in α1D^−/− mice. We conclude that α1D can form LTCCs with negative activation thresholds essential for normal auditory function and control of cardiac pacemaker activity.