Patients with advanced malignancy are at an increased risk of cardiac arrhythmias, from their cancer and cardiotoxic treatments. Supportive care products co-administered should therefore not increase this risk. No clinically important cardiovascular effects are associated with the administration of granisetron over 30 s. To determine the effects of a rapid (1 s) injection of granisetron, 3 mg, on measures of cardiac repolarisation, a pilot study was performed in 17 patients undergoing moderately/highly emetogenic chemotherapy at two centres. All received dexamethasone, 8-12 mg, infused over 30 min, followed immediately by granisetron and then chemotherapy. Twelve-lead electrocardiograms (ECGs) performed before granisetron treatment, 2 h later and the following day (11 patients) showed no differences in QTc(end max), QTc(apex max) or QT-interval dispersion between baseline and subsequent measurements, and there were no significant secondary adverse events. On this basis, granisetron should be considered the first-choice antiemetic for patients at increased risk of cardiac complications.