The aim was to investigate the propagation of Ca2+ waves between cells and determine whether this synchronizes alternating Ca2+ release between cells. Experiments were carried out on electrically coupled cell pairs; spontaneous Ca2+ waves were produced by elevating external Ca2+. There was a significant difference in the ability of these waves to propagate between cells depending on the orientation of the pairs. Although almost all pairs connected by side-to-side contacts showed propagating Ca2+ release, this was very uncommon in end-to-end cell pairs. Confocal studies showed that there was a gap at the intercalated disc consisting of cell membranes and a region of cytoplasm devoid of sarcoplasmic reticulum. This gap was 2.3 μm in length and is suggested to interfere with Ca2+ wave propagation. The gap measured was much smaller between side-to-side contacts: 1.5 μm and so much less likely to interfere with propagation. Subsequent experiments investigated the synchronization between cells of Ca2+ alternans produced by small depolarizing pulses. Although this alternation results from beat-to-beat alternation of intracellular Ca2+ wave propagation, there was no evidence that propagation of Ca2+ waves between cells contributed to synchronization of this alternans.