Complete hemodynamic evaluation of patients with combined aortic and mitral mechanical valve prostheses presents a difficult technical problem. Yet such patients with cardiac symptoms postoperatively often require this evaluation to determine the diagnosis and the advisability of reoperation. A 4 year experience with 22 patients requiring such evaluation is reviewed. Eight patients (36 percent) required reoperation for malfunction of the prosthesis. Four (18 percent) had major complications of the cardiac catheterization study, but no fatalities or residual permanent defects resulted. In 17 cases transthoracic left ventricular needle entry was used. A standardized procedure of this type for both pressure measurement and angiographic studies has evolved, providing reasonable efficiency and a relative degree of safety. The patient is positioned in the right anterior oblique position for optimal needle entry into the left ventricular apex and angiographic visualization of mitral prosthetic incompetence and the myocardial contractile pattern. A 16 gauge needle with side holes but no end hole allows ventriculography to be performed after chamber entry using the prostheses as reference points under fluoroscopic guidance. Retrograde catheterization of the aortic prosthesis, transseptal left atrial catheterization with anterograde crossing of the mitral prosthesis and transapical pressure measurement with a similar needle, combined with quantitative left atrial angiography, are alternative choices for study.