Electrocardio-graphic (ECG) signals such as the standard 12-lead are synthesized from a novel reduced electrode set. Signals are received from a group of electrodes connected to predetermined locations on a human body, and deriving at least one further ECG signal using predetermined transformation(s) (130) on said first set of ECG signals. This forms a desired set of signals. The group of electrodes may comprise the standard 12 lead electrode sites V2 and V5 plus one electrode positioned substantially level with V5 on the right anterior axillary line, and a further electrode on each of the right hand side and left hand side of the body. In an alternative arrangement the electrode position V2 is replaced by an electrode position Vc on the sternum directly between the standard electrode sites V1 and V2. Also disclosed is a method of improving accuracy of synthesized signals by detecting body posture and modifying the transformations.