The magnetic fields caused by the human heart's electrical activity were coherently recorded with a biomagnetic multichannel system (KRENIKON) during 1 to 10 minutes in 49 patients. 31 to 37 magnetic channels were recorded simultaneously with the ECG and respiration. Comparison of a magnetic index and the Sokolow-Lyon index to echocardiographic findings in the quantification of left ventricular hypertrophy demonstrated the superiority of the magnetocardiogram (MCG) as compared to the ECG. The magnetocardiographic investigation of patients with WPW-Syndrome, ventricular extrasystoles, ventricular tachycardia, and paced ventricular beats demonstrated that multichannel magnetocardiography permits the non-invasive three dimensional localization of arrhythmogenic tissue with high spatial accuracy.