Today, cardiac contractility in mice is exclusively measured under anaesthesia or in sedated animals because catheters available are too rigid to be used in the awake mice. We have there-fore developed a new catheter (Pebax03) to measure cardiac contractility in conscious mice. In this study we have evaluated the accuracy and utility of this new catheter for assessment of cardiac contractility in anaesthetized and conscious mice. Using a balloon pop test, the pebax catheter with an inner diameter of 0.3 mm was found to exhibit a high natural frequency, a low damping coefficient and a flat frequency of up to 50.5±0.6 Hz. Under anaesthesia (0.5 or 1.0% halothane), no difference was found in heart rate (HR), left ventricular systolic pressure (LVSP), LVdP/dt_max, LVdP/dt_min, ejection time (ET), and isovolumic relaxation ( en measured either with the 1.4F Millar or the pebax 03 catheter. However, when HR, LVSP,LV dP/dt_max and LVdP/dt_min were recorded with the pebax catheter in awake mice, values were significantly higher and ET and lower than under anaesthesia suggesting a major impact of anaesthesia on these parameters. The pebax catheter was also used in a normotensive one-renin gene mouse model of cardiac hypertrophy induced by DOCA and salt. In this model, DOCA/salt induced a severe decrease in cardiac contractility in the absence of changes in blood pressure. These data demonstrate that cardiac contractility can be measured very accu-rately in conscious mice. This new device can be of great help to investigate cardiac function in normal and genetically engineered mice.