Before, I say anything, let me say that very low carb diets in my opinion have a place in the diets of some men with certain medical conditions, such as obesity and potentially cancer and diabetes. However, I do not seem them working for the majority of men long term and have outlined some of the big issues that these diets need to overcome: poor gut health in some men; very high LDL counts in some men; decreased athletic performance for medium and high intensity exercise in most men, etc. And, more recently, very low carb diets appear to be on the receiving end of another black eye from breaking research that shows that very low carb diets may actually subtly damage the heart and appear to have a significant side effect in many men (and women) of arrhythmias.
Now, again, I am NOT saying that all men on a very low carb diet have heart damage and arrhythmia. However, I am saying that it looks like the risk factor for the same may be increased and so one should do their own research and discuss with a good doc if he/she wants you on this diet long term.
Browsing around the Paleo and Low Carb forums, you will see that some members complain of this issue. For example, one Reddit member wrote: “About four months ago, (after 3 months in ketosis) I went into arterial fibrillation out of the blue. I’ve never had heart problems save for a occasional missed beats (one every week or less) that I always chalked up to anxiety. (I have anxiety disorder) Blood tests were performed, and I was found to be slightly dehydrated, with microcytic anemia, but all other indicators were normal. I was shocked back into rhythm and sent home. I immediately discontinued my diet and have not had any heart issues since.” 
Now notice what this member wrote – that he was checked for dehydration. This is what I see as I am reading: low carb advocates are saying that the issue must be related to things like dehydration or mineral deficiencies, etc. In actuality, it is nothing as benign according to one study at least: the ketones actually interact with the heart itself in a very negative way. As you know, those on a ketogenic diet end up with high levels of ketones. High ketone levels are not all bad and have some good properties. Unfortunately, it looks like your heart doesn’t like too many of them!
For example, one recent study looked at children with diabetes who sometimes die from irregular heart beats (arrhythmias). Scientists initially thought it might be electrolyte imbalances, but they found instead that is was the high amount of plasma ketones that these children had.  The researchers said that anyone with significant ketoacidosis, the technical name for when our body has to break down fat for energy, over an extended period of time may be vulnerable to this. Of course, those on very low carb diets all fall into this category, but alcoholics and, as mentioned above, diabetics can be as well. Again, it is very important to point out that these patients did NOT have electrolyte or any other known issues.
NOTE: I also recommend scanning my page on Low Carb Diets and Heart Disease, where I discuss the recent evidence that Low Carb Diets can accelerate arterial plaque (atherosclerosis) in some men (when not losing weight) and cause heart damage after a heart attack.
So is it really all that bad? Well, recent animal studies show that it may actually be much worse long term, at least for some men. One researcher fed animals (rats) a 60% fat, 30% protein and 10% carbohydrate diet. What they found was surprising when they took these animals through a heart attack and then bring them back again. Basically, the low carb animals had fat in their heart, which lead to a larger heart attack, due to “due to ventricular arrhythmias and hemodynamic shock.”  The researchers pointed that, after a heart attack, the all important left ventricular function was decreased.
Now this study did point out that there were no real differences prior to the heart attack. However, this only shows that in the short term, men might not notice any issues on very low carb diets. The results, at least in animals, clearly show that heart function is definitely being altered and, long term, may not be such a wise idea. It also says that if you are one of the unlucky ones to have a heart attack, you may be at greatly increased levels of risk from a very low carb diet.
Furthermore, some studies show that low carb diets can increase inflammation and one study showed that increased fibrinogen levels. Again, this would be particuarly dangerous in a heart attack scenario. For details, see my page on Low Carb Diets and Inflammation. You can also find more about Low Carb Diets in my Summary Page on Diet and Nutrition.