In avian and mammalian embryos, surgical ablation or severely reduced migration of the cardiac neural crest lead to a failure of outflow tract septation known as persistent truncus arteriosus (PTA) and, to embryo lethality due partly to impaired excitationcontraction coupling stemming primarily from a reduction in L-type Ca²⁺ current (I_Ca,L). Decreased I_Ca,L occurs without a corresponding reduction in the 1 subunit of the Ca²⁺ channel. We hypothesize that decreased I_Ca,L is due to reduced function at the single channel level. The cell-attached patch clamp with Na⁺ as the charge carrier was used to examine single Ca²⁺ channel activity in myocytes from normal hearts from sham-operated embryos and from hearts diagnosed with PTA at embryonic days (ED) 11 & 15 after laser ablation of the cardiac neural crest. In normal hearts, the number of single channel events per 200 msec depolarization and the mean open channel probability (P_o) was 1.89 ±0.17 and 0.067±0.008 for ED11 and 1.14±0.17 and 0.044±0.005 for ED15, respectively. These values represent a normal reduction in channel function and L-type Ca²⁺ current observed with development. However, the number of single channel events was significantly reduced in hearts with PTA at both ED11 and ED15 (71% & 47%, respectively) with a corresponding reduction in P_o (75% & 43%). The open time frequency histograms were best fitted by single exponentials with similar decay constants ( 4.5 msec) except for the sham at ED15 (=3.4 msec). These results indicate that the cardiac neural crest influences the development of myocardial Ca²⁺ channels.