Magnetocardiography (MCG), which uses a multi-channel superconducting quantum interference device (SQUID), is applicable to the non-invasive analysis of ischemic heart disease and arrhythmia. MCG systems that use a low-temperature superconductor (LTS)-SQUID enable the measurement of cardio-magnetic fields across a wide age range, from fetus to mature adult, and are capable of detecting very weak signals because the magnetic sensor is sensitive to signals above a few fT/ (Hz)1/2. Abnormalities in the current distribution of an ischemic heart and the propagation pathway for arrhythmia are thus easily detected and visualized. In the area of next-generation products, 16-channel and 32-channel high-temperature superconductor (HTS)-SQUID systems are also being developed to realize more compact systems. Some open-ended cylindrical magnetic shields were applied to HTS- and LTS-MCG systems. These cylindrical shields made a uniform magnetic field in the light magnetic shielding, and environmental noise was easily cancelled due to the uniform magnetic field inside the shielding. An improvement in HTS-SQUID sensitivity and a noise reduction technique have made real-time MCG measurement possible.