He was taken to the National Institute of Cardiovascular Diseases or NICVD on Wednesday night, said Mushtuq Husain, a leader of the Jatiya Samajtantrik Party or JaSoD.
The 80-year-old has been suffering from high blood pressure and other complexities.
Serajul had undergone a heart surgery and heap transplant earlier, but was not comorbid, said Mushtuq, a former general secretary of Dhaka University Central Students’ Union or DUCSU.
Dr Mir Jamal Uddin, a physician at the NICVD, said Serajul has breathing problems, lung infection and heart complications.
“It’s difficult to say what condition he is in now because he is an aged person. We will conduct more tests tomorrow (Thursday),” the doctor said.
A confirmed bachelor, Serajul is now living with his brothers in Dhaka’s Kalabagan after a long stay in the US, said Mushtuq.
Serajul and other student leaders formed a network called ‘Nucleus’ in the early 60s to push for Bangladesh’s independence from Pakistan.
Soon after the creation of Bangladesh, the Awami League suffered a split and the splinter group became JaSoD under the guidance of Serajul.
He never held any top post of any political party, but became known as the mentor of the JaSoD leaders.
He also avoids public appearances and speeches, which has made his behind-the-scenes activities mysterious.