The Food and Drug Administration is warning about serious heart risks from a popular antibiotic.
Z-Paks are used to treat common infections, and are sold under the brands "Zithromax" and "Zmax."
The FDA says the drug can interfere with the heart's electrical activity, disturbing its rhythm and possibly having fatal consequences.
The elderly and people with irregular heart beats are at the highest risk.
Despite the warning, experts say not to stop taking the medication without talking to your doctor.