The invention relates to determining a representation of cardiac output in a patient. Provided are a method and a system for monitoring a cardiac output using a single device inserted into a Central Venous Catheter (CVC) or Peripheral Inserted Central Catheters (PICC) line. In an embodiment, the device contains an elongated body that fits the lumen of a Central Venous Cava or Peripheral Inserted Central Catheters line and has an ultrasound transducer at the tip. By operating the device such that the velocity in both the Superior Vena Cava and Inferior Vena Cava can be sampled continuously the CO is monitored.
