Electrocardiograms were recorded from bottlenose dolphins using an IBM compatible laptop computer with a 80486 DX2(50) processor, a Princeton Applied Research model 113 preamplifier and a "Smart Heart" 3 lead personal heart rate monitor with windows-based software. Soft pliable 7.5 cm diameter suction cups with embedded 2.5 cm diameter silver contacts and shielded lead wires were used as electrodes. Hewlett Packard redux paste was used as an electrode gel. Skin was cleaned by gentle rubbing prior to placing the electrode. The red lead was placed on the dorsal surface of the left pectoral flipper, the white lead was placed on the dorsal surface of the right pectoral flipper, and the black lead was placed on the dorsolateral trunk in line with the insertion of the flippers. The preamplifier setting for low frequency roll-off was 30 Hz and the high frequency roll-off was set at 300 Hz. An additional ground from the animal to the white lead input was sometimes necessary to eliminate disruptive 60 Hz interference and or unknown EMF interference from passing ships and unknown sources.