Computed tomography (CT) is a powerful imaging tool for generating clinically useful information.Iodinated contrast medium (ICM) is usually used to enhance the imaging intensities and the tissue contrast, anyway it can cause a variety of adverse reactions. Ionic ICMs are associated with more serious reactions than non-ionic ICMs, but the Bureau of National Health Insurance only pays for the use of ionic ICM with CT in Taiwan, except for certain specific indications. The goal of our study is to develop a real-time method for monitoring patients who received rapid intravenous injection of ionic ICM during CT examination. Sixty-seven patients were enrolled in this study (aged 48�13 years, mean�SD), comprising 38 males (aged 47�11 years) and 29 females (aged 48 �14 years), who received CT examinations with intravenous bolus injection of iothalamate meglumine. A standard pulse oximeter was used to detect the heart rate (HR) changes that were considered to represent the response to the ionic ICM. The results showed that the HR per minute ros e rapidly to peak and then re turned to baseline slowly. Patients felt much discomfort when there was rapid increase in HR or when the HR-recovery time is longer. Moreover, the HR-increase after intravenous injection of ionic ICM is greater in younger patients under 50 years than in older patients. We conclude that an oximeter can be used to reliably monitor the pathophysiologic condition of patients and the discomfort related to tachycardia during a rapid intravenous injection of ICM for CT.