Abstract: A method of determining the blood flow characteristics from a monitoring signal indicative of blood flow in the vicinity of a heart, the method including the steps of: (a) extracting a flow envelope from the monitoring signal; (b) extracting a series of temporal markers from the flow envelope. (c) removing extraneous flows such as valve opening and closing flows from the flow envelope; (d) extracting features from the flow envelope and monitoring signal, such as peak velocity; (e) Producing cardiac parameters based on said monitoring signal.