The veteran leader was 80 years old.
According to local media reports, Reddy was on his way to Manali to attend a parliamentary standing committee meeting on Friday when he suffered the attack.
He was rushed to a government hospital in Shimla, where he is reported to have passed away.
Telangana Chief Minister K Chandrasekhar Rao expressed shock and grief over the Congress leader’s sudden demise.
Offering condolences to the bereaved family, the Chief Minister’s Office said that KCR had directed Chief Secretary SP Singh and Resident Commissioner Arvind Kumar to make arrangements to bring Reddy’s mortal remains back to Hyderabad from Kulu.
The official Twitter handle of the Congress party also extended condolences to his family.
Reddy was born on November 19, 1936 at Nadimpally village in Mahabubnagar district. He had completed his Bachelors degree from Osmania University.
Reports say that he had been elected to the Legislative Assembly of both Andhra Pradesh before bifurcation, and Telangana after bifurcation, five times.
He had also served one term as a member of the Legislative Council in 1979. He was first elected as an MLA in 1967, and became an MP in 2012. He had also served as a state minister.
According to his profile on the government portal, he had visited a number of countries including the Commonwealth Nations, USA and Canada on behalf of the Andhra Pradesh Commonwealth Parliamentary Association.
He had also toured China, South Korea, Thailand, Malaysia, Singapore and Hong Kong on behalf of Andhra Pradesh Legislative Assembly to study agricultural and industrial development in 2003.