Fox Tampa Bay reports his retirement goes into effect Wednesday at 5 p.m.
"Because of recent unexpected health issues and after much consideration and reflection, I have submitted my retirement. I have been honored and humbled to serve as the Chief of Police for the past seven months," said Chief Rieser in a statement.
Rieser stepped into the role earlier this year after the former chief Bernadette DiPino resigned.
He grew up in Sarasota and joined the Sarasota Police Department in 1992. During his time with the agency, he was awarded a Life-Saving Medal, Distinguished Service Medal, and Meritorious Service Medal.
City officials appointed Deputy Chief Rex Troche as interim police chief. Troche joined the agency in 2002 and served as an officer or supervisor in four agency divisions, including criminal investigations.