Spontaneous Ca2+ transients in rat pulmonary vein cardiomyocytes are increased in frequency and become more synchronous following electrical stimulation

•Pulmonary vein cardiomyocytes possess T-tubules.•Ryanodine receptors were distributed as striations and along cell periphery.•Asynchronous spontaneous Ca2+ transients present between those that were electrically evoked.•Raising extracellular Ca2+ concentration increased frequency of spontaneous Ca2+ transients.•The wave velocity and synchronisation of spontaneous Ca2+ transients was also increased.