QT Interval Prolongation Associated With Cytotoxic and Targeted Cancer Therapeutics Opinion statement Cardiovascular toxicities are potentially serious treatment limiting complications of many different cancer therapeutics including traditional cytotoxic chemotherapies as well as targeted- and immunotherapies. As a result, there is increased monitoring for cancer treatment-related cardiotoxicities, ranging from heart failure to arrhythmias. Many anticancer treatments are known to prolong the QT interval through a variety of mechanisms including direct effects on ion channels and indirectly via intracellular signaling pathways. While QT prolongation increases the risk for the potentially life-threatening ventricular arrhythmia torsades de pointes, the incidence of this arrhythmia in the setting of most cancer treatments is quite rare, and the majority of patients can continue safely receiving these medications despite their QT prolonging potential. A multidisciplinary approach to the cardiovascular care of the cancer patient is essential to mitigate risk of cardiotoxicity while minimizing unnecessary treatment disruption of potentially life-saving cancer treatments.