A bipolar, single-lead electrocardiogram (ECG) device is capable of recording ECGs with an integrated smartphone application. To determine the utility of this device, phone-based ECGs (pECG) were compared with standard six-lead ECGs (sECG) in four female Atlantic bottlenose dolphins (Tursiops truncatus) at the National Aquarium. Study animals were trained to haul out onto a dry deck in ventral recumbency and allow simultaneous 30-sec ECG acquisition using the two devices. The pECG device was held against the thoracic wall caudal to the left axilla. The sECGs were recorded in the frontal plane. Instantaneous heart rates were obtained from identical QRS complexes on both ECGs. Three boarded cardiologists independently evaluated the rhythm and the polarity of the QRS depolarization for each recording and the results were compared. The mean heart rate was 80 beats/min (range 62–92 beats/min) and 80 beats/min (range 60–92 beats/min) for the pECG and sECGs, respectively. All four dolphins displayed sinus respiratory arrhythmia, and one animal had occasional atrial premature contractions. Rhythm diagnosis and QRS polarity were identical for the pECG and sECG. Dolphin vocalizations created artifacts on the pECG that were not present on the sECG, so pECGs had to be acquired without vocalization. The pECG appears to be an accurate and useful method to monitor the heart rate in Atlantic bottlenose dolphins. This system is inexpensive and portable, making it valuable for health examinations, transport monitoring, and stranding responses.