Athenahealth President and CEO Jonathan Bush has resigned , effective immediately.

Executive Chairman Jeff Immelt and CFO Marc Levine will assume responsibility for day-to-day operations. Board member Amy Abernethy, MD, PhD of Flatiron Health will advise the company on data strategy.

Bush was the subject of misconduct allegations and the pressure of activist investor Elliott Management.

Athenahealth’s board is exploring a sale, merger, or other transaction involving the company, but will also consider continuing as an independent company. It has opened a search for Bush’s replacement as CEO.

Bush said in the announcement, “I believe that working for something larger than yourself is the greatest thing a human can do. A family, a cause, a company, a country – these things give shape and purpose to an otherwise mechanical and brief human existence. Athenahealth is a near once-in-a-life time example of such a thing. With that lens on, it’s easy for me to see that the very things that made me useful to the company and cause in these past 21 years are now exactly the things that are in the way. I cannot imagine a single organization more loaded with potential to transform healthcare.”

Board Chair Jeff Immelt said, “Athenahealth is the most universally connected healthcare network in the country and we believe there remains significant, unrealized value in the company. To ensure Athenahealth maximizes shareholder value and is best positioned to realize the full potential of its premier healthcare technology platform, the board has authorized a thorough evaluation of strategic alternatives, including a potential sale or merger or continuing as an independent company under new leadership. We approach this process with an open mind and a commitment to continuing to strengthen the company – including its rich data asset, platform strategy, and culture of innovation. We are fully focused on serving the best interests of our shareholders, employees and clients.”