To examine the underlying mechanism of AF-mediated growth arrest, we used flow cytometry to analyze levels of the DNA damage marker, phosphorylated H2AX at serine 139 (γ-H2AX), as well as levels of cleaved poly-ADP ribose polymerase (PARP), which is a marker of apoptosis, in MDA-MB-468 and Cal51 parental cells. The gene discussed is H2AX; the disease is atrial fibrillation.