In a statement, the Spanish club said that Laso, 54, was admitted to Madrid's Sanitas La Moraleja University Hospital after "suffering a myocardial infarction" earlier in the day.
Real Madrid later said that Laso underwent "a catheterisation procedure" following the heart attack and he is now stable.
It added that Laso "will spend the night under observation in the intensive care unit" at the hospital.
Spanish national Laso, who is a former basketball player, has been coaching Real Madrid since 2011.
Under him, the Whites won Turkish Airlines EuroLeague titles in 2015 and 2018 and the Spanish league five times.
Laso was also honored with the EuroLeague Coach of the Year award in 2015 and 2018.
