A medical magnetometer (10) comprising one or more induction coils (2) for detecting a time varying magnetic field of a region of a subject's body, such as the heart. Each coil has a maximum outer diameter of 4 to 7 cm, and a configuration such that the ratio of the coil's length to its outer diameter is at least 0.5, and the ratio of the coil's inner diameter to its outer diameter is 0.5 or less. Each induction coil (2) is coupled to a respective detection circuit comprising a low impedance pre-ampiifier (3), a low pass filter (5), a notch filter (6) to remove line noise, and an averaging element (7). Each detection circuit produces an output signal (9) for use to analyse the time varying magnetic field of the region of the subject's body.
