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Percutaneous transluminal balloon valvuloplasty is a new technique in interventional cardiology which to date has been applied successfully in the dilatation of all four cardiac valves. Although the different techniques appear to be quite effective, the safety of these procedures has not been fully explored. In particular, because of the close anatomic relationship of the aortic and mitral annuli, the safety of aortic valvuloplasty in patients with mitral valve prosthesis is unknown. Therefore, we report the applicability of a percutaneous double balloon valvuloplasty in an elderly patient with calcific aortic stenosis and a Bjork-Shiley mitral valve prosthesis.

Many enzymes are subject to allosteric control, often with inhibitors and activators binding to the same effector site. Phosphofructokinase in Escherichia coli is such an enzyme, being inhibited by phosphoenolpyruvate (PEP) and activated by ADP and GDP. How do individual interactions with effectors affect the balance between activation and inhibition, especially when both ligands share aspects of the same binding site? We find that mutation of a single residue in the effector site, Glu----Ala 187, leads to PEP being an activator rather than an inhibitor. With low concentrations of the substrate fructose-6-phosphate, the mutant enzyme is more than one hundred times more active than wild-type enzyme at millimolar concentrations of PEP. The classical Monod-Wyman-Changeux two-state model is too simple to account for the properties of the mutant enzyme.

Electronic pacing is now the accepted therapy for patients with symptomatic slow ventricular heart rates. Pacing may be temporary or permanent, epicardial or endocardial, fixed, synchronous or demand. The choice of pacing mode is dictated by the clinical status of the patient, his progress during temporary pacing, and the presence or absence of competitive rhythm.

RADIOCHROMIUM HAS THESE ADVANTAGES FOR THE MEASUREMENT OF WHOLE BLOOD VOLUME: it remains in the erythrocytes many hours; it can be measured easily and accurately; the amount of radiation from it is very low.As measured by the radiochromium method, the whole blood volume of normal patients was determined to be 65.6 cc. +/- 5.95 cc. per kilogram of body weight or 2.49 +/- 0.28 liters per square meter of body surface. In a majority of a series of patients with heart disease, hypervolemia was found during right ventricular failure but not in those having left ventricular failure or mitral stenosis alone.