Medical devices and methods for making and using medical devices are disclosed. An example system for mapping the electrical activity of the heart includes a catheter shaft. The catheter shaft includes a plurality of electrodes including a first and a second electrode. The system also includes a processor. The processor is capable of collecting a first signal corresponding to a first electrode over a time period and generating a first time-frequency distribution corresponding to the first signal. The first time-frequency distribution includes a first dominant frequency value representation occurring at one or more first base frequencies. The processor is also capable of applying a filter to the first signal or derivatives thereof to determine whether the first dominant frequency value representation includes a single first dominant frequency value at a first base frequency or two or more first dominant frequency values at two or more base frequencies.