Voltage-dependent facilitation of L-type Ca²⁺ channels is an important regulatory mechanism by which excitable cells modulate Ca²⁺ entry during a train of action potentials. Expression of the α₁ and β subunits of the α_1C Ca²⁺ channel is necessary and sufficient to reproduce this kind of facilitation in Xenopus oocytes. Here we show that, by expressing the α_1C together with different β subunits in oocytes, the β₁, β₃ and β₄, but not the β₂ subunits are permissive for Ca²⁺ channel facilitation. The poor facilitation observed in rat ventricular cells, together with the presence of the β₂ subunit mRNA, suggest that β₂ may be the β subunit associated with functional cardiac L-type Ca²⁺ channels.