The introduction of ionizing radiation in medicine revolutionized the diagnosis and treatment of disease and dramatically improved, and continues to improve, the quality of health care. Cardiovascular imaging and medical imaging in general are, however, associated with a range of radiobiologic effects, including, in rare instances, moderate to severe skin damage resulting from cardiac fluoroscopy. For the dose range associated with diagnostic imaging (corresponding to effective doses of the order of 10 mSv (1 rem)), the possible effects are stochastic in nature and largely theoretical. The most notable of these effects is, of course, a possible increase in cancer risk. The current review addresses radiobiology relevant to cardiovascular imaging, with particular emphasis on radiation induction of cancer including consideration of the linear non-threshold dose-response model and of alternative models such as radiation hormesis.