Female nurses having irregular working hours for more than six years, are upto 70 per cent more prone to heart attacks than their male counterparts. This was revealed by Ichiro Kawachi and his colleagues at the Harvard Medical School, USA. Researchers attribute the hazards of this profession to the stress-related hormones which are released while nurses perform their duties. Disruption of the body's daily biological clock results in the secretion of hormones which play havoc with the heart.