Sharif, who is serving a seven-year imprisonment in a Lahore jail, was rushed to a hospital on Tuesday after he complained of heart related complications.
Sharif, 69, was taken to the Punjab Institute of Cardiology (PIC) Lahore from Kot Lakhpat Jail in high security.
He was discharged from hospital and taken back to jail following medical tests.
"According to Mr Sharif's medical tests (conducted on Tuesday), his condition is not serious. But, he needs aggressive medication and regular medical follow-ups to avoid cardiac complications, a senior doctor told Dawn.
He said Sharif's angiography might be conducted.
Sharif's stress thalium test -- a nuclear imaging test that shows how well blood flows into one's heart -- suggests "post stress LV pump/contraction 56 per cent which is almost normal", the report said.
The report says that the left ventricle, the main pumping chamber of the heart, is damaged on the lower left wall, it said.
Expressing concern about Sharif's health, his daughter Maryam tweeted: "My only source of information on what is happening to my father is the media only."
Sharif's brother Shahbaz Sharif asked the government to provide best healthcare facilities to the three-time prime minister.
A special medical board that examined Sharif in jail last week observed "he is not completely well" as more investigations (tests) are required before suggesting treatment for him.
According to the report of the special medical board, "Patient Muhammad Nawaz Sharif, 69, examined by the special medical board is a known case of diabetes Mellitus and hypertension for the last 10 years. He is also known case of Ischemic heart disease since 2001."
Sharif underwent Coronary Angioplasty (PCI) twice in 2001 and 2017. He also had open heart surgery twice in 2011 and 2016 (no medical record/documents are available for these above said procedures at the time of examination), it says.
The board says after evaluating these test reports and availability of previous cardiac medical record further management plan will be proceeded.
Sharif was shifted to the Kot Lakhpat jail on December 25, a day after he was sentenced by the accountability court in Islamabad to seven years' imprisonment in the Al-Azizia Steel Mills case.
A disqualification of 10 years from holding any public office is part of the sentences awarded to the three times prime minister of the country.