Chemicals can alter the number of beats per minute, even in animals other than humans. Daphnia are small freshwater creatures with transparent bodies, which means you can watch their hearts directly under a microscope. You dissolve three over-the-counter medications into separate water solutions — pseudoephedrine (a decongestant), aspirin (a pain reliever), and Benadryl (an antihistamine) — then place new groups of daphnia in each one. A video camera attached to the microscope records the heartbeats in slow motion, and comparing each group to the plain-water control shows which drugs speed the heart up and which slow it down.

Different drugs produce different effects on the body — and daphnia make those effects visible. These small freshwater creatures have a transparent body, so their hearts can be watched beating under a microscope. Three over-the-counter medications — pseudoephedrine (a decongestant), aspirin (a pain reliever), and Benadryl (an antihistamine) — were each dissolved into separate water solutions. Groups of daphnia were placed in each solution, and their heart rates were compared to a control group in plain water to see which drugs sped the heart up and which slowed it down.

Their transparent body makes daphnia uniquely useful for testing how substances affect a living body. You can watch their heart beat directly under a microscope, with no dissection required. When you dissolve common over-the-counter medications — pseudoephedrine, aspirin, and Benadryl — into separate water solutions and record heart rates, each drug's effect on a real heartbeat becomes measurable. The control group in plain water gives you a baseline, and slow-motion video playback from a camera attached to the microscope makes counting heartbeats precise.