Sitagliptin increased plasma glucagon-like peptide-1 ( 7-36 ) levels and , at peak stress , enhanced both global ( ejection fraction , 70.57.0 versus 65.78.0 % ; P < 0.0001 ; mitral annular systolic velocity , 11.72.6 versus 10.92.3 cm/s ; P = 0.01 ) and regional left ventricular function , assessed by peak systolic velocity and strain rate in 12 paired , nonapical segments .