Lily-of-the-valley, clematis and chrysanthemums are attractive plants that can make your heart soar. Problem is, they're also capable of shutting it down.

All are commonly cultivated plants that are toxic if ingested by people or pets.

Just as many plants have the ability to heal, so thousands of ornamental plants have complex chemical compositions that make them capable of poisoning, said Michael Balick, vice president and director of the Institute of Economic Botany at The New York Botanical Garden.

"The concept of poison and the concept of medicine are closely aligned," he said. "You're usually talking about dosage."

Digitalis is a prominent example, said Balick, co-author of the "Handbook of Poisonous and Injurious Plants" (The New York Botanical Garden Press and Springer, 2007). "A certain dosage of the digitalis leaf could enable the pumping of the heart, where a larger dosage could kill a person," he said.

There were 60,514 cases of unhealthy plant exposure reported in 2007 to the nation's poison control centers, according to the federal Health Resources and Services Administration.

"This includes all routes of exposure, including swallowing plants, and skin reactions from such plants as poison ivy and poison oak," said David Bowman, an agency spokesman. Plants were cited in two fatalities.

Toxic plants do not pose as much danger as pharmaceuticals, but it pays to be cautious.

"Some plants can cause severe oral irritation if chewed," Bowman said. "Mistaking hemlock for carrots has been responsible for seizures and fatalities."

Many houseplants also are toxic.

"Chewing dieffenbachia or philodendron could cause oral irritation and swelling," he said. "Some other common indoor plants like African violet, jade plant and sansevieria are not poisonous but could cause stomach upset if swallowed."

If poison ivy or poison oak plants are burned, people inhaling the smoke could suffer the same ill effects in the respiratory tract as contact with the plants causes to the skin.

Reactions to plant toxicity range from minor to lethal, and also depend upon a person's health and age.

"Some people are more sensitive to things in the environment than others," said Rosie Lerner, an extension horticulturist with Purdue University.

Body weight plays a part, she said. Generally, the smaller the body, the less toxin required to make you ill.

"This is one reason why children are so vulnerable," she said. "An individual's metabolism also may play a role."

Proximity to poisonous plants doesn't mean people should shy away from gardening, Lerner said.