Sano and colleagues (2002) have shown that CDK9 expression is upregulated and activity is enhanced during cardiac hypertrophy, and that chronic activation of CDK9 predisposes to heart failure in adult mouse myocardium. More recently, CDK9 has been shown to act as a binding partner of GATA4, an important regulator of cardiomyocyte proliferation in mammals and zebrafish (Kikuchi et al., 2010). This link to GATA4 provides support for a possible role of CDK9 in regulating cardiomyocyte proliferation (Sunagawa et al., 2010). Here, CDK9 is linked to heart failure.