Q fever, caused by <i>Coxiella burnetii</i>, is a bacterial zoonosis with a wide clinical spectrum that can be life-threatening and, in some cases, can become chronic.

The presence of an abnormality of cardiac function that is responsible for the failure of the heart to pump blood at a rate that is commensurate with the needs of the tissues or a state in which abnormally elevated filling pressures are required for the heart to do so. Heart failure is frequently related to a defect in myocardial contraction.