[en] Ionizing radiation (IR), as frequently used in modern oncology, has been accused to cause chronic cardiotoxic side effects. Since little is known about the possible underlying pathomechanisms of those detrimental radiation-dependent effects, we tested whether IR acutely affects isolated cardiac myocytes. We conclude that IR acutely affects cardiac myocytes in vitro due to an elevated [ROS]_i induced by IR. The resulting changes in Ca cycling may reflect an early, IR-dependent stress-like-reaction in cardiac myocytes, possibly mediated through an ROS/CaMKII-dependent pathway. Since disturbed Ca homoeostasis contributes to the development of several cardiac diseases, we conclude that the acute, IR-dependent effects with respect to cardiac myocytes may contribute to the long-term, detrimental effects of ionizing radiation with respect to the heart