Inclusion Criteria:

          -  Must have adequate coagulation, hematology, kidney, and liver function, per protocol.

          -  Diagnosis of relapsed or refractory (R/R) acute myeloid leukemia (AML)

          -  Meet the following disease activity criteria:

          -  an established, confirmed diagnosis of AML by World Health Organization criteria
             excluding acute promyelocytic leukemia (APL)-M3; and

          -  an Eastern Cooperative Oncology Group (ECOG) performance status less than or equal to
             2.

          -  If male participant is sexually active, he must agree from day 1 through 6 months
             after the last dose of alvocidib or 90 days after the last dose of venetoclax,
             whichever is longer, to practice the protocol-specified protection.

        Exclusion Criteria:

          -  History of any malignancy within the last 6 months except for those specified in this
             protocol and low-grade malignancies not requiring active treatment such as
             non-melanoma skin cancer, cervical intraepithelial neoplasia, or prostate cancer in
             situ.

          -  Prior allogeneic stem cell transplant within 6 months of study drug administration and
             no requirement for graft versus host therapy.

          -  History of previous enrollment in Studies NCT02993523 or NCT03069352.

          -  History of exposure to alvocidib or any other cyclin-dependent kinase 9 (CDK9)
             inhibitor.

          -  History of Tumor Lysis Syndrome (TLS) due to previous exposure to venetoclax.