ECG electrode placement from Scaling of heart rate with breathing frequency and body mass in cetaceans

Example of electrode placement on a bottlenose dolphin (A) and a killer whale (B). For the bottlenose dolphin, two electrodes were placed on the ventral side of the animal in line with the top edge of the pectoral fins (one on each side) and the third electrode was placed on the left side approximately 15 cm below the other two electrodes. For the other species, the electrodes were placed in a vertical line down the center of the ventral side of the animal between the pectoral fins approximately 10 cm apart.