The heart is a contractile organ that can generate its own rhythm. The contraction, or the rhythm, of the heart may be influenced by electromagnetic field (EMF) exposure, because of the heart's excitability characteristic. In previous studies, different methods have been used to study the possible effects of an extremely low frequency electromagnetic field (ELF-EMF) on the heart. But the studies' designs were not similar, and the results were also different. Recent studies have shown some evidence that short-term EMF exposure can influence the heart more than long-term exposure. This study investigated how the heart is affected in the first EMF exposure. In a simulation of the daily exposure of humans to a power frequency, Wistar albino rats were used. By utilizing the Helmholtz-coil set, we obtained a 50-Hz, 1-mu T EMF and examined rat heart activity during short-term EMF exposure. No effect was observed under this exposure condition. The results obtained do not confirm a possible mechanism in the electrical activity of the rat heart model.