ECGs are often given to people thought to have had an attack of angina, a condition characterized by sharp chest pains that is a common symptom of coronary artery disease.
Angina is experienced by about 1 in 50 people in Britain, where the study was conducted.
The ECG test is administered by placing electrodes on the skin and recording the electrical activity of the heart over time to check for abnormal rhythms.
It has been shown to be effective in detecting damage, but its ability to predict future heart disease was unknown, according to the study, published in the British Medical Journal.
A team of researchers led by Adam Timmis, a professor at the London Queen Mary's School of Medicine and Dentistry, studied 8,176 patients with suspected angina and no prior history of heart disease.
All the patients received a standard clinical assessment, looking at criteria including age, sex, ethnicity, duration of symptoms, description of chest pain, smoking status, and history of hypertension and medicines.
They also received an ECG while they were at rest. In addition, some 60 percent of the patients had what is called an exercise ECG, performed while they were in motion.
All the subjects were monitored over the following year.
The researchers found that nearly half of all heart incidents that occurred during that period happened in patients whose ECG tests had given no indication of heart disease.
A routine clinical assessment, they found, was almost as good a predictor of future heart problems.
"These findings are a reminder of the importance of taking a detailed history and making a thorough physical examination," wrote Beth Abramson, director of Saint Michael's Hospital in Toronto, in a commentary, also in the British Medical Journal.
"The additional information from the ECG is helpful in some patients but does not predict risk in everyone."