As fasting is one of the principle duties in many religions, coronary heart disease patients often ask, “Is it possible for me to fast ?” or “Would fasting be harmful for my heart?” A definite answer for this question is still controversial. We have found that plasma viscosity increased significantly in ischaemic patients in correlation to normal subjects (P value = 0.014). Plasma viscosity is significant higher in diabetic and hypertensive patients in comparison to non diabetic and normotensive subjects respectively. Fasting results in insignificant increase in plasma viscosity in diabetic and hypertensive patients in comparison to non diabetic and normotensive subjects respectively.