An automatic ambulatory electrocardiogram analyzer was developed using a self-powered fast reader of FM recorded cassettes and a "general purpose" microcomputer with 640 Kbytes of RAM and 20 Mbytes of mass memory on hard-disk. Original algorithms were developed for analog to digital conversion, data storage on hard-disk, QRS detection and classification and rhythm analysis. Reliability of the system was evaluated, when appropriate, using standard databases. The relevant features of our analyzer include a favourable cost/benefit ratio, powerful interactive facilities and the typical flexibility of the non dedicated hardware.