Daniel Vasella, CEO of Novartis AG, is in charge of 98,000 employees in 140 countries at his giant drug and health-care-products company, which had $38.1 billion in revenue last year. Yet for all his authority, he sometimes feels like a prisoner — to his calendar.

"I'm locked in," he says. He is booked nearly solid until September, with back-to-back meetings and trips that were scheduled months ago. "Due to the constraints, I have to put down in priority things I like to do and that would be very interesting. I can't spend as much time as I'd like to at hospitals, talking with doctors and patients who use our products. This is where I hear and see so much and get so many ideas."

Other CEOs are equally chained to crammed agendas. They complain about a lack of spontaneity in their workdays and little time to mull over problems that crop up. They often have to make do with phone calls and e-mails, when a face-to-face meeting might be more effective.

Far more than their predecessors, top executives face many demands from many different people. "Where CEOs a decade ago may have had five choices, they have 100 — and because they're under more scrutiny, they're more pressured to be visible and make themselves available," says Richard Wellins, senior vice president of global marketing at DDI, a Pittsburgh-based consultant.

To start with, executives are at the helm of much larger companies than existed even a short time ago. They spend considerable time globetrotting to visit employees and customers dispersed around the world. They are expected to stay in close touch with a growing list of constituents — from directors and big investors to government regulatory officials and potential business partners. They're also in demand to serve as directors of other companies and other organizations, to appear on television, to give speeches at universities, to headline conferences, and to participate in nonprofit and civic groups.

"With each request, I have to make a judgment about whether this is something important for the company, something I'd enjoy doing, or something I want to do to help someone else," says Vasella.

He keeps himself in check by occasionally stepping back to evaluate his plans, questioning whether he could do his job differently. When he has to give presentations to analysts, he asks himself whether they really add to sales and earnings.

Like Vasella, Mark Hurd, CEO of Hewlett-Packard, thinks meetings with customers are crucial to expanding the bottom line and shouldn't be sacrificed. He tries to visit at least one customer whenever he is traveling for another purpose.

The problem is that it is impossible to predict months in advance, when trips are being planned, which customers will be most important to see. So he makes sure he has some breathing space on his calendar. He leaves some time each day for things that just come up. That can be anything from a call from an executive at another company to an impromptu meeting with one of his own managers.

Planning downtime for unexpected meetings isn't easy for executives on the go. Kathleen Murphy, CEO of ING US Wealth Management, says her calendar is booked a year ahead for national sales conferences, meetings of several nonprofit boards she sits on, and meetings she holds every quarter with employees in different parts of the United States. She spends about 60 percent of her time traveling.

These days, she looks forward to the time she has for herself on planes. "No one can reach me by phone, and I can get reading and thinking done," she says.

When she is back at her office in Hartford, Conn., she has to find a way to quickly catch up and then move ahead. She often schedules meetings in half-hour intervals during her workdays, which typically are 12 hours long.

"I ask pointed questions to make sure (subordinates) know I'm focused on what is driving the business," she says. "It's not about keeping them on their toes but about having meetings that matter."

The single most crucial element for surviving such a schedule, she believes, is to have a competent team to which you can delegate important jobs. "At my level, you can't get caught in the weeds," she says, "you have to move back to a more strategic position."