The Downton Abbey legend, 77, was reportedly hospitalised after suffering severe chest pains and was taken to a specialist cardiac unit at the private Wellington Hospital in London, according to Britain's Sunday Mirror.
The publication added that she underwent a series of tests and was later released.
However, a spokesperson for Smith insists the star is in good health, saying, ""She is fine and well at home.""
It is believed the actress visited the clinic for a routine medical procedure.
Smith suffered a health setback in 2007 when she was diagnosed with breast cancer, but she has since made a full recovery.