Ronald Chigunwe worked for Wessex Heartbeat, which supports the cardiac centre at Southampton General Hospital.
The 40-year-old, of Breadels Field, Basingstoke, pleaded guilty to four offences of fraud and money laundering.
However, he denied four other charges of money laundering. The Crown Prosecution Service will now decide whether he should face trial.
A decision is due within the next 14 days.
The fraud was uncovered when a new chief executive took over at the charity and became suspicious after asking Chigunwe for financial information.
The chief executive's wife - an accounts expert - was asked to look at the records and discovered the fraud.
A former financial controller has admitted stealing more than £440,000 from a hospital charity.