The E2F-family of transcripion factors exerts fascinating and contrasting functions in tran-scriptional repression and activation of genes regulating proliferation, apoptosis, and differentiation. E2F is principally regulated by its temporal association with retinoblastoma pocket protein (pRb) family members. In turn, pRb is regulated through phosphorylation by cyclin-dependent kinase (cdk). The activity of cdk is negatively regulated by cdk-inhibitors, exemplified by p16INK4a , p21CIP1 , and p27KIP1 . Therefore, positive and negative signaling events converge on E2F activity resulting in distinct growth-controling and apoptotic activities. Here we describe the immunocytochemical detection of E2F, genomic DNA, BrdU-incorporation, and mitosis in cardiomyoctes. A detailed protocol is given to illustrate this technique in primary heart muscle cells.