Dr Kevin Fong talks to Dr Bruce Martin , an anaesthetist at University College London Hospital, about the hazards of keeping patients safely anaesthetised during heart surgery. Anaesthetic drugs disrupt heart rhythm and reduce blood pressure, which can push diseased hearts over the edge and cause cardiac arrest. Dr Martin also demonstrates a new ultrasound technique (transoesophageal echocardiography or TOE) that can be used to watch patients' hearts in action