Extraordinary weight gain may be an initial finding in some patients with peripartum cardiomyopathy (PPCM). This case highlights the need for studies of the relationship between degrees of antenatal weight gain and risk of PPCM. A 33-year-old woman exhibited weight gain of 1.0 kg/week (38.5–60.6 kg) between gestational weeks (GW) 12+2 and 33+2 at which dyspnea appeared. Her body weight further increased to 69.1 kg at GW 34+2 at which echocardiography revealed left ventricular dysfunction (ejection fraction = 27%, fractional shortening = 4.0%). She then lost 24 kg in body weight by 4 weeks postpartum.