The Connecticut chief medical examiner’s office has determined that Berkeley senior Andrew Kroon’s death last spring was caused by cardiomegaly, an enlarged heart, said Lorraine Siggins, the chief psychiatrist at University Health Services.

Kroon was found dead April 16 in his room in the Taft Apartments. Siggins said the medical examiner’s report states that the manner of death was natural.

Kroon’s father Richard expressed relief about the final announcement of the cause of death.

“When Andrew died, the police department reported his death as an apparent overdose,” Richard Kroon said. “Toxicology results didn’t show fatal levels of anything.”

The autopsy showed that Kroon died from a congenital heart defect that was surgically corrected at birth, Kroon’s father said. The medical examiner, he said, found fluid in Kroon’s lungs in addition to his abnormally large heart, a sign that his heart was working much harder than normally expected.

The specific congenital heart defect from which Kroon suffered is known as a transposition of the great vessels. People with this condition have their two major vessels exiting the heart — the pulmonary artery and the aorta — reversed, said James Perry, the chief of pediatric cardiology at the Yale School of Medicine. The condition upsets the path that blood would normally travel and is life-threatening, he said.

When Kroon was two weeks old, his father said, he had surgery performed at the Boston Children’s Hospital to correct his condition. The surgery — known as the Senning procedure — follows the maxim “two wrongs make a right,” Perry said. In the procedure, a baffle, which creates a tunnel between the two atrial chambers, is constructed to change the flow of blood in the heart to make up for the fact that the vessels are reversed, he said. But the process is far from perfect.

“Their right ventricle can fail down the road,” he said. “They can get heart failure, and some get a very dangerous tachycardia.”

Perry said people like Kroon need to be watched because they may not even realize they are developing heart failure. Some of the people need pacemakers or even repeat surgery, he said.

Over the past two decades, the Senning procedure has been phased out and replaced by a new procedure, Perry said. Surgeons now do an arterial switch operation, he said, in which a surgeon cuts off the aorta and pulmonary artery of a one-week-old baby and reverses them. This procedure was not perfected when Kroon had his operation and had a high rate of mortality.

“Now we expect every baby to do great,” Perry said.

The use of surgical operations to repair congenital heart disease began largely at Yale, Perry said. Yale-New Haven Hospital has also started a program, now in its early days, called the Adult Congenital Heart Program, where adults born with heart defects can be continually followed throughout their lives.