Severe mitral regurgitation was associated with cardiogenic shock in five (0.8%) of 623 patients with acute myocardial infarction who were urgently admitted to the authors' hospitals between 1994 and 1996. The infarct was located in the inferior wall in four patients and in the inferoposterior wall in one patient. Severe mitral valve regurgitation occurred concurrently with cardiogenic shock between one and six days after the onset of myocardial infarction. A mitral regurgitant murmur was not audible in four of five patients. Similarly, mitral regurgitant Doppler signals were not detected in four patients by transthoracic echocardiographic examination, while transesophageal echocardiographic examination detected mitral regurgitant signals clearly in all patients. Thus, when cardiogenic shock is unexpectedly associated with inferior or inferoposterior wall acute myocardial infarction, severe mitral regurgitation should be suspected, even when a mitral regurgitant murmur is not audible. Furthermore, mitral regurgitant flow signals may not always be detected by transthoracic echocardiography. Thus, examination for mitral regurgitation by transesophageal echocardiography should be considered.