Tenofovir is a nucleotide analog reverse transcriptase inhibitor approved for the treatment of HIV and hepatitis B infections. It is widely prescribed and an integral part of the recommended regimens for the treatment of HIV infection in antiretroviral-naive patients. Tenofovir is implicated in renal proximal tubular dysfunction, which can be associated with Fanconi syndrome and hypokalemia. When the hypokalemia is severe, it can lead to life-threatening complications. We describe the case of a 59-year-old woman who suffered a cardiac arrest secondary to severe hypokalemia from tenofovir use.