It is not uncommon for patients to have cardiovascular or respiratory problems when they consult physicians. As a medical assistant, you may be responsible for performing screening and/or diagnostic testing in the physician's office. To correctly perform testing on the cardiac or respiratory system, you need to review the anatomy and physiology of the heart and the respiratory system. This chapter introduces you to the electrocardiograph instrument and how to administer an electrocardiogram. You will also learn how to apply electrocardiograph electrodes and wires, operate the instrument, and troubleshoot problems that can occur while recording the heart's electrical activity. Because many physicians perform more complex cardiac diagnostic testing, you will also learn about Holter monitors and stress testing. Pulmonary function testing is more commonplace now in physician's offices, and this chapter introduces you to the basics of performing a spirometry.