Abstract— This paper describes a methodology for beat detection in the electrocardiographic signal, ECG, from laboratory mice. The configuration and setup of the equipment used for signal acquisition has been done considering the particularities of the animals involved and the further studies to be done.  The presented approach is based on the combined use of filters, Wavelet transforms and adaptive threshold detectors. This methodology was used in studies of the effect of drugs in heart rate variation, and allowed the detection of 100% of QRS-T complexes as long as the estimation of QT intervals in one-lead records. The use of the presented approach in studies that uses more than one lead could improve the overall results.