The effects of testosterone in humans and other vertebrates occur by way of two main mechanisms: by activation of the androgen receptor (directly or as DHT), and by conversion to estradiol and activation of certain estrogen receptors. Free testosterone (T) is transported into the cytoplasm of target tissue cells, where it can bind to the androgen receptor, or can be reduced to 5alpha-dihydrotestosterone (DHT) by the cytoplasmic enzyme 5alpha-reductase. The areas of binding are called hormone response elements (HREs), and influence transcriptional activity of certain genes, producing the androgen effects.
Adverse effects of testosterone supplementation may include increased cardiovascular events (including strokes and heart attacks ) and deaths based on three peer-reviewed studies involving men taking testosterone replacement.  In addition, an increase of 30% in deaths and heart attacks in older men has been reported.  Due to an increased incidence of adverse cardiovascular events compared to a placebo group , a Testosterone in Older Men with Mobility Limitations (TOM) trial (a National Institute of Aging randomized trial) was halted early by the Data Safety and Monitoring Committee .  On January 31, 2014, reports of strokes , heart attacks , and deaths in men taking FDA-approved testosterone-replacement led the FDA to announce that it would be investigating the issue.  Later, in September 2014, the FDA announced, as a result of the "potential for adverse cardiovascular outcomes", a review of the appropriateness and safety of Testosterone Replacement Therapy (TRT).    The FDA now requires warnings in the drug labeling of all approved testosterone products regarding deep vein thrombosis and pulmonary embolism . 
Keep in mind that using enanthate this way will cause a significant build up of testosterone in the bloodstream that will not cease to increase until four or five weeks of injections. This is due to the fact that taking a four hundred milligram injection, and another four days later, still has at least 200mg working from the previous dose. The third injection then adds another four hundred and the first is still not entirely used up. You may realistically have over a gram or so in the bloodstream before you know it. Just be careful, and keep this in mind when figuring out your dosages.