Introduction Daphnia magna are small fresh water creatures commonly known as “water fleas”. This species can be normally found in lakes, rivers and ponds. Furthermore, Daphnia play a significant and utterly essential role in in aquatic food chains, a stepwise transfer of energy in the form of food. They eat different types of food such as yeast, algae and bacteria. On the other hand, Daphnia are also the prey of a variety of predators such as, small fish, Hydra, tadpoles and aquatic insects. These water fleas are living organisms and therefore it’s important to test the reactions of the heart rate. Different studies have shown the effect of the Daphnia heart rate depending on what substance was tested. For example, a few years ago it was discovered that there was a minor heart increase when the Daphnia was tested with 2 Mm of caffeine but then later the heart decreased (Campbell et. Al 2004). In another study, it was found that the ethanol substance slowed down the heart rate due to the possible interference with the normal procedure of heart rate regulation (Bonnie Kaas, Kithira Krishna Rao, Elizabeth Marion, Larissa Stuckey, and Rebecca Kohn 2009). Also, a study found that when nicotine was applied to Daphnia there was stimulation and reticence depending on the concentration of ethanol. A high concentration of alcohol caused the heart rate to accelerate while a low concentration induced a slow heart rate (E.R Baylor 1948). In this experiment I got to look at the effect of ethanol on the heart rate of a Daphnia creature. Although I didn’t know what substance I was testing, I had hypothesized that ethanol would make the heart rate slow down; therefore, the null hypothesis is that ethanol will have no significant effect on the heart rate. Materials and Methods The Daphnia magna was collected from a nearby pond. When I arrived at my Biology lab on February 11 the Daphnia was stored in a container with spring water. The individu