The strict regulation of our heart rates allows our bodies to adapt to changing conditions to provide the different parts of our bodies with the appropriate amounts of oxygen and nutrients. Cardiac arrhythmias, or irregularities in the heart rate, can have devastating consequences such as heart attack or stroke. Understanding the basis for heart rate regulation may improve our current ability to treat and prevent cardiac arrhythmias. Voltage-gated potassium (Kv) channels are proteins in the heart tissue that play a critical role in the regulation of heart rate. Kv channels open and close depending on the electrical activity with in the heart. By allowing potassium ions to exit the heart muscle cells, Kv channels indirectly regulate whether the cells (and hence heart) will contract, or beat. After the channels open, they often undergo a process known as inactivation which causes the channel to close and prevents potassium flow. The rate at which channels enter and exit inactivation plays an important role in determining heart rate. May Cheng is studying the inactivation properties of two Kv channels found in the heart, Kv1.5 and Kv4.2. Kv1.5 has been implicated in atrial fibrillation, and Kv4.2 is believed to play a role in ventricular fibrillation. By increasing our understanding of the basic processes behind potassium channel inactivation, this research may lead to future therapies to treat cardiac arrhythmias.