In order to identify the cause of maternal deaths due to thrombotic thrombocytopenic purpura (TTP) and identify future preventative measures we retrospectively reviewed all maternal deaths due to TTP in London from 2003 to 2008 that were confirmed on post-mortem examination. There were three maternal deaths due to sudden cardiac arrest within 1, 5 and 2 days of presentation, respectively. Post-mortem findings revealed they all died with intramyocardial microvascular thrombosis, the thrombi being characteristically platelet rich (CD61+, fibrin−). Platelet thrombi in the coronary microvasculature are the cause of early sudden death in TTP in pregnancy. If TTP cannot be excluded in the differential diagnosis of thrombotic microangiopathies of pregnancy, then plasmapheresis should be instituted as a medical emergency. ADAMTS-13 levels are helpful in making the diagnosis, but results should not be awaited before instituting plasmapheresis.