In Japan, cardiovascular diseases are frequent complications in cancer patients owing to the rapidly aging population and changes in the overall lifestyle. In addition, new anticancer therapies have substantially improved the prognosis of cancer patients. Cardiotoxicity, also referred to as cancer treatment-related cardiac dysfunction, has become an important cause of morbidity and mortality in cancer patients. Cardiotoxicity may consist of hypertension, arrhythmia, thromboembolism, coronary artery disease, valvular disease, and left ventricular dysfunction which may progress to heart failure. Close interactions between cardiologists and oncologists are required for the optimal care of many cancer patients. Although cardiologists are expected to assist and advise the oncologist by providing diagnostic and prognostic information regarding developing cardiotoxicity, little is known about the cardiovascular pathogenic mechanisms associated with cancer treatment. Onco-cardiology is a medical subspecialty that focuses on the diagnosis and treatment of cardiotoxicity in cancer patients. This review describes the concept of onco-cardiology, and focuses on the management of cardiotoxicity that may arise during or after cancer therapy from the standpoint of cardiology. We also discuss noninvasive diagnostic options to identify and characterize cardiotoxicity.