Using a microelectrode technique we studied the effects of vascular endothelial growth factor-B on the activity of rat atrial myocardium under normal conditions and after gradual stretching of the tissue. It was shown that vascular endothelial growth factor-B increased duration of the action potential only at the level of 90% re-polarization. Effects on the frequency and force of contraction were absent. The repetition frequency of the action potentials did not change. Close observation of the vascular endothelial growth factor-B-induced mechanisms and stretch-induced alteration in action potential durations to 90% of repolarization, confirmed the existence of a link between the examining growth factor-B and stretch induced mechanisms.