Hearts have confirmed that manager Craig Levein was taken to hospital on Monday morning and is "recovering well" after receiving medical treatment.
The reason for the 53-year-old being rushed to hospital is not known.
Levein, who is in his second spell as Hearts manager, watched on as his side beat Kilmarnock on Saturday to climb to the top of the Scottish Premiership table.
Assistant boss Austin MacPhee has been placed in charge of first-team duties until Levein returns.
A statement on the club's official website read: "Having received medical treatment, Craig is now recovering well in hospital.
"No further comment will be made at this time and the club asks that Craig and his family's privacy be respected, as we all wish him a speedy recovery."
Levein returned to Tynecastle in 2014, initially working as director of football before replacing sacked Ian Cathro last year.
