The women, all previously healthy, were taking fenfluramine and phenter- mine, or fen-phen, a popular combination of diet pills, when they developedan unusual and serious heart valve problem. Eight of them also had a po-tentially fatal condition in which the arteries that supply blood to the lungsconstrict. The women sought medical attention because they had such symptoms of heart problems as fatigue, shortness of breath and fluid accumulation inthe ankles or abdomen. Doctors then made the connection to the diet drugs,although they have not clearly shown cause and effect. The observations, made in the normal course of medical practice rather than in clinical studies, cannot be used to estimate the risk of the diet pills.But F.D.A. officials said they were concerned, and quickly warned doctorsto be on the lookout for heart problems in patients taking the drugs.