Usage patterns
一心に〈動詞〉to do [verb] wholeheartedly/single-mindedly
She was praying with all her heart.
一心に働くto work single-mindedly, devoting oneself entirely to the task
My father worked tirelessly and single-mindedly for the family.
一心に見つめるto gaze intently at something
The child gazed intently at his mother's face.