Idiopathic MVP is characterized by a late systolic click or murmur from myxomatous mitral valvular dysfunction. It may be complicated by atypical chest pain, ventricular arrhythmias, and ECG changes that can mimic the symptoms of coronary artery disease. We prospectively performed radionuclide cineangiograms before and after stress tests in MVP patients with chest pain compared with asymptomatic MVP patients and symptomatic normal control patients. In ten patients with MVP, chest pain, and normal coronary anatomy, the LVEF remained essentially unchanged (increase of -0.5 +/- 4 percent) after exercise. In ten patients with MVP and no chest pain and in nine with normal cardiovascular system and chest pain, the exercise LVEF increased by 11.5 +/- 2 percent (p less than 0.05) and 17.4 +/- 3 percent (p less than 0.005), respectively. The resting LVEF was significantly lower (p less than 0.02) in the symptomatic MVP patients (59 +/- 3 percent) than in the asymptomatic MVP (76 +/- 5 percent) or symptomatic normal patient control subjects (70 +/- 3 percent). Patients with MVP and chest pain had a lower resting LVEF and an abnormal left ventricular functional response to exercise compared with asymptomatic MVP patients or symptomatic normal subjects. Therefore, exercise radionuclide ventriculography may not adequately differentiate between chest pain due to MVP or coronary artery disease.