  We characterize the extreme heartbeat star system MACHO 80.7443.1718 in the
LMC using TESS photometry and spectroscopic observations from the Magellan
Inamori Kyocera Echelle (MIKE) and SOAR Goodman spectographs. MACHO
80.7443.1718 was first identified as a heartbeat star system in the All-Sky
Automated Survey for SuperNovae (ASAS-SN) with $P_{\rm
orb}=32.836\pm0.008\,{\rm d}$. MACHO 80.7443.1718 is a young (${\sim}6$~Myr),
massive binary, composed of a B0 Iae supergiant with $M_1 \simeq 35 M_\odot$
and an O9.5V secondary with $M_2 \simeq 16 M_\odot$ on an eccentric
($e=0.51\pm0.03$) orbit. In addition to having the largest variability
amplitude amongst all known heartbeats stars, MACHO 80.7443.1718 is also one of
the most massive heartbeat stars yet discovered. The B[e] supergiant has Balmer
emission lines and permitted/forbidden metallic emission lines associated with
a circumstellar disk. The disk rapidly dissipates at periastron which could
indicate mass transfer to the secondary, but re-emerges immediately following
periastron passage. MACHO 80.7443.1718 also shows tidally excited oscillations
at the $N=25$ and $N=41$ orbital harmonics and has a rotational period of 4.4
d.
