We find that cdk2 activity is maintained at substantial levels throughout the cell cycle (Sumerel et al., 2001), but in addition it rises abruptly to reach a peak (19-fold over unfertilized levels) at 4 min AF, correlating with the early peak in ERK1 activity (Philipova et al., 2005a). This evidence concerns the gene CDK2 and atrial fibrillation.