Captopril (CP; 1-[(2s)-3-mercapto-2-methyl propionyl]-L- proline), an orally active inhibitor of angiotensin-converting enzyme (ACE) [1,2], is in many countries the medication of choice for the management of hypertension and is often used to treat some types of congestive heart failure [3-6]. The gene discussed is ACE; the disease is congestive heart failure.