In the United States there are now approximately 521 marathons, and in 2005 approximately 432,000 participants completed one. The number of frequent runners (more than 100 days a year) is estimated at over 11 million. When one of these patients presents to the emergency department with cardiac complaints, the risk profile and evaluation may be different than in sedentary subjects. The first and most important step to patient evaluation is the history. An electrocardiogram (ECG) should be obtained in all patients with suspected cardiac complaints. Depending on the study and what is defined as abnormal, 40-80% of athletes' ECGs will show some abnormality. A normal ECG has a 96% negative predictive value for ruling out structural cardiovascular abnormalities, but a positive predictive value for disease of only 7%. The electrocardiogram, cardiac enzymes, and stress testing are useful, but should be interpreted in the context of the sport and the athlete. Echocardiography and cardiac magnetic resonance imaging are indicated for the diagnosis of certain conditions. Cardiology consultation or inpatient evaluation may be indicated when a specific disease process is suspected based on history, physical examination, or ECG. Some patients may require follow-up for further diagnostic testing.