The coexistence of valvular incompetence and of a cardiac left to right shunt presents diagnostic difficulties, especially when the latter is not suspected clinically. Systemic arterial indicator dye dilution curves characteristic of left to right shunts may be modified and masked by the effects of the accompanying valvular regurgitation, as demonstrated in the three patients described. A reduced cardiac output state may produce the same effect. The double catheter technic has been well defined in the past, but its application as a screening procedure in patients with valvular incompetence and/or a low output state, clinically unsuspected of left to right shunt, has not been stressed. The authors advocate this as a routine step during cardiac catheterization to avoid diagnostic errors.
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