External Ca²⁺ influx via L-type Ca²⁺ channels is required for EC coupling in hESC-CMs.

<p>A. Confocal line-scan images from a representative, field-stimulated hESC-CM under control conditions (i.e. 1.8 mM external Ca²⁺, upper image) and after the application of a Ca²⁺-free solution (lower). B. Corresponding [Ca²⁺]_i transients under control (black trace) and Ca²⁺-free (red) conditions. C. [Ca²⁺]_i transients before (black) and after the application of the L-type Ca²⁺ channel blocker diltiazem (10 µM, red).