Patients with cancer can experience adverse cardiovascular events secondary to the malignant process itself or its treatment. Patients with cancer might also have underlying cardiovascular illness, the consequences of which are often exacerbated by the stress of the tumour growth or its treatment. With the advent of new treatments and subsequent prolonged survival time, late effects of cancer treatment can become clinically evident decades after completion of therapy. The heart's extensive energy reserve and its ability to compensate for reduced function add to the complexity of diagnosis and timely initiation of therapy. Additionally, modern oncological treatment regimens often incorporate multiple agents whose deleterious cardiac effects might be additive or synergistic. Treatment-related impairment of cardiac contractility can be either transient or irreversible. Furthermore, cancer treatment is associated with life-threatening arrhythmia, ischaemia, infarction, and damage to cardiac valves, the conduction system, or the pericardium. Awareness of these processes has gained prominence with the arrival of strategies to monitor and to prevent or to mitigate the effects of cardiovascular damage. A greater understanding of the mechanisms of injury can prolong the lives of those cured of their malignancy, but left with potentially devastating cardiac sequelae.