RT Journal Article SR Electronic T1 Adaptation of the maternal heart in pregnancy JF British Heart Journal JO Heart FD BMJ Publishing Group Ltd and British Cardiovascular Society SP 540 OP 543 DO 10.1136/hrt.68.12.540 VO 68 IS 12 A1 Stewart Hunter A1 Stephen C Robson YR 1992 UL http://heart.bmj.com/content/68/12/540.abstract AB