The mini organs, which beat of their own accord, have been developed specifically to look at heart hypertrophy - where the heart muscle thickens, making it harder to pump blood around the body.
Researchers at Abertay University in Dundee are using the tiny hearts to test potential drugs they hope could eventually allow them to stop it developing in those at risk.
Made from stem cells, the tiny hearts are just 1mm in diameter and contract at about 30 beats per minute.
Although healthy to begin with, scientists are using chemicals to make them hypertrophic, or enlarged, due to abnormal growth of heart cells.
Once diseased, they are then treated with newly-developed medications to see if they can prevent damage from occurring.
The team said that human hearts have been grown in labs before, but this is the first time it has been possible to induce disease in them.
Lead researcher Professor Nikolai Zhelev said: "Heart hypertrophy can be hereditary, can be caused by diseases such as diabetes or can be caused by doing too much strenuous exercise.
"In some people, a life-threatening abnormal heart rhythm will develop and this is the most common cause of sudden death in young people. Although there are treatments, these only help to control the symptoms and there is no known cure."
It works by using biosensors to label specific molecules in the hearts to see where they are going.
The team has been able to target the drugs and stop molecules going down the path they would usually take - preventing hypertrophy.
Prof Zhelev, who will present the research at a conference in Spain today, said several drugs were being tested, and one drug, which is being trialled in cancer treatment, has given positive results.
"Although heart cells are the only ones in the body that will never get cancer, we noticed the pathways the molecules in hypertrophic hearts follow are similar to those followed by molecules in cancerous cells, so we thought testing this new drug on these hearts might have the same positive effect," he said.
"And this has certainly proved to be the case."