Autonomic blockade by propranolol and atropine to study intrinsic myocardial function in

activity by an intravenous injection of 0.2 mg/kg pro-pranolol and 0.04 mg/kg atropine was used with cardiac catheterization to study intrinsic cardiac function in 47 patients with normal hearts and known graded myo-cardial disease. After blockade, significant hemodynamic abnormalities became apparent at rest in the majority of patients with known disease, many of whom had normal control findings. This occurred partly through a reduction in the normal range of cardiac function at rest, and partly through changes in the abnormalities as-sociated with disease: after blockade, diseased hearts had normal stroke volumes, but beat more slowly, and had higher left ventricular filling pressures. The heart rate after blockade was fixed; this was defined as the in-trinsic heart rate (IHR); it ranged from 57 to 126 beats/ min in different patients. Both the IHR and left ven-tricular end-diastolic pressure after blockade were sensi-tively and quantitatively related to the severity of myo-cardial disease. When, after blockade, arterial pressure was raised by angiotensin, the IHR was unchanged; normal hearts maintained their stroke volume and in-creased stroke work; diseased hearts maintained stroke volume less well and stroke work was unchanged or fell. Abnormal ventricular responses corresponded well with abnormal ventricular function at rest. In different patients the IHR was significantly re-lated to each available index of left ventricular function. Other studies in animals have shown that the IHR is closely related to intrinsic myocardial contractility in certain forms of experimental heart failure. An anal-ogous relationship existing between the IHR and myo-cardial function in patients with heart disease is sug-gested as the explanation for the IHR/ventricular func