In the year 1900, the maximum number of deaths occurred due to infectious and communicable diseases. The top killer was pneumonia or influenza (202.2/100000 deaths), followed by TB (194.4/100000 deaths) and the third spot taken by gastrointestinal diseases (142.7/100000 deaths). The treatment of these diseases required a general improvement in sanitary conditions, health and hygiene. The main mode of curing these diseases would be by prescribing the relevant antibiotics in the case of pneumonia, prescribing the cocktail of drugs to cure TB and usage of antibiotics as well as maintaining the fluid and salt levels in the body in the case of gastrointestinal diseases. Currently, we find that the whole spectrum of diseases affecting humans in the U. S. A. has undergone a radical change. Due to improvement in health and sanitation, the infectious diseases are reduced to a small minority in the overall scheme of diseases that affect humans. They are not as serious as they were in 1900. In the year 2000, heart disease has emerged as the main killer disease (192.9 /100000 deaths) followed by cancer (185.9 /100000 deaths). This is a drastic increase from the 1900 levels, especially for cancer as only 64 / 100000 deaths were due to cancer in 1900. Overall the number of deaths has significantly reduced from 1900 levels and the life expectancy of the population has consequently improved. In this scenario, the above two diseases are even more important in maintaining the health of the population. What has to be kept in mind here is that the two diseases above are not infectious diseases, there is no pathogen that has to be eliminated or killed to save the patient. Rather, these two are lifestyle diseases. Heart disease is caused by a number of factors, chief of which are our sedentary lifestyle, lack of exercise, poor diet, consumption of junk food, smoking etc. similarly, the types of cancers are many. Most of the cancers caused can be related to the presence of a large number of carcinogens present in our environment. A person who is suffering from heart disease or cancer has not only to be cured of it, but once the person is cured, there has to be a life long follow up of the person. With increasing life expectancy, the care needed for the person and the expenses to be met are all going up placing a lot of strain on limited resources available with the individual and the government. The human genome project has revolutionized biology. A complete database of a person’s DNA make up is now available. For eg. In the case of cancer, scientists have been able to identify oncogenes present in the human genome. Scientists are able to also understand the genetic factors behind diseases including heart disease. By looking into the genome of a person, it is possible to pinpoint the chances of a person developing a particular disease at a particular stage of his/ her life. The doctor can then propose changes or steps to be taken to minimize the chances of that par.