％我
\documentclass[ aspectratio = 1610 ]{beamer}
\usepackage{amsthm}
\usepackage{amsmath}
\usetheme{Frankfurt}
\makeatletter
\setbeamertemplate{theorem begin}{%
\begin{\inserttheoremblockenv}%
{\inserttheoremheadfont\ifx\inserttheoremaddition\@empty\else\inserttheoremaddition\fi}%
}
\setbeamertemplate{theorem end}
{\end{\inserttheoremblockenv}}
\makeatother
\begin{document}
\begin{frame}
\begin{definition}[ Is it possible to produce this heading without the white bar below?]
\end{definition}
\end{frame}
\end{document}