2. Cardiac rhythm and autonomic function assessment: Heart rate variability (HRV) reflects the modulation of the heart by the autonomic nervous system, and it can be quantified using several different methods based on analysis of the temporal changes between successive heartbeats. The development of autonomic dysfunction in breast cancer patients has been shown in a few small clinical studies, but the majority of these studies have considered HR rather than HRV, which is a much less robust measure of autonomic function. The few studies that have used HRV analysis have demonstrated significant reductions in HRV following the completion of anthracycline-based therapy. Previous research on other ECG markers (e.g. QT and QRS duration) in breast cancer patients has mainly focused on anthracycline-based regimes; the influence of trastuzumab treatment on ECG makers has been evaluated in only two studies to date. It is still not clear whether these changes can predict subsequent LV dysfunction although QT variability is a possible marker of myocardial contractility and has been shown to increase as a result of anthracycline therapy in breast cancer patients. This study aims to characterise the impact of different treatment regimes on the temporal properties of the ECG and will compare beat-to-beat QT variability and beat-to-beat T wave variability in breast cancer patients receiving a range of treatment regimes.