“What are the first few steps in case of a cardiac arrest?”

First thing, loosen the clothes. Lay him on the floor, check the airway and pulse, call for help (911) and start CPR, if you are familiar.

For any person that falls unresponsive, we need to move and try to call them. If no response, call the ambulance. Cardiac compressions need to be started promptly.

The very first step is to call 911. You want to initiate getting trained medical professionals to that person as quickly as possible and then having those professionals transport that person to an emergency department. Our EMS professionals, Fire - EMS - Police are trained and drill in critical life saving steps needed top provide the most life sustaining outcomes.
Personally, the greatest thing you could do now is to take a CPR course offered by the American Red Cross ( https://www.redcross.org/take-a-class/cpr ) or from the American Heart Association (http://cpr.heart.org/AHAECC/CPRAndECC/FindACourse/UCM_473162_Find-A-Course.jsp ). These are excellent, state of the art courses that will provide the tools needed to provide the best care possible out-side-of-a-hospital for an individual suffering from a heart attack.
Finally, in general, until help arrives: place the person in a safe comfortable place, work on getting them to calm down and to breath comfortable and easily. Loosen any tight restrictive clothing and if they have medication for their heart that they are supposed to take (generally a small nitroglycerin pill that goes under their tongue) help them take that medication. They're likley to vomit so only a sip of water at best and otherwise nothing to eat or drink. Thats about the best you can do without CPR training, which is the next thing you should do now to increase the odds of a good outcome, if necessary, in the future.

If you are experiencing chest pain, I would advise taking an aspirin and going to the nearest emergency department! If you feel weak or don’t have a safe ride, call 911 for an ambulance. If you delay, you could suffer a “cardiac arrest” and die.
You asked what to do in a “cardiac arrest.” This implies that the patient is already unconscious and without a palpable pulse. In that case, start CPR, call 911, and ask for a defibrillator (if available).

This is a difficult question to answer, for one reason. We are all different -- I think of it as we are all wired differently. Because of that, there are a significant percentage of patients who do not present with the classical symptoms that we read about in books. For example, some patients never have any pain when they are having a heart attack (AMI FOR SHORT). They may only feel tired, or feel short of breath. The key is to prevent the AMI from happening, which means seeing your doctor, your PCP, regularly. Know what your risk factors are for having heart disease. Here is a list of risk factors that increase your likelihood of having an AMI, or heart disease. A family history, especially if people in your family have heart attacks at a young age, like 30-50 years old. This is probably the worst risk factor you can have and can't change. Smoking, having uncontrolled high blood pressure, high cholesterol, being overweight, not exercising at all, and having a poor diet, one that is high in fat. The classic symptoms of a heart attack, or AMI, are chest pain in any area of the chest, especially if the pain gets worse with exertion and gets better with rest. Other symptoms include shortness of breath, chest pain that radiates down either arm, or to the neck or back; getting sweaty with the chest pain is a bad sign. Nausea and vomiting are also possible symptoms. If you or anyone starts having these symptoms, don't wait and hope they will go away - ESPECIALLY IF YOU HAVE SEVERAL RISK FACTORS - go to your Dr. or to the ER. If someone has cardiac arrest in front of you, the first thing to do is have someone call 911, then hopefully someone has taken some type of CPR class. Check for a pulse, check to see if they are breathing, if their chest is rising and falling; if it isn't and there's no pulse, start CPR until an ambulance can get there. I recommend that all family members who have any risk factors at all take at least a basic CPR course.
Cardiac disease can be very tricky, even for a Board Certified ER Dr., again, because not everyone has textbook symptoms. I have personally found 2 patients over my >20 year career who complained of a toothache, but something about them wasn't right. I asked them cardiac questions, we did an EKG, and they were both in the midst of having a heart attack. So I never let my guard down when it comes to this diagnosis. Hope that helps.

-Call for help (911)
-Check for response
-Check neck pulse and breathing at the same time.
-If no pulse, begin CPR (chest compression = push fast and push hard, center of the chest). Don't stop until EMS gets there.

Sudden death may occur for a Ventricular Fibrillation in most cases. You have less 4 /5 minutes to cardioversion. You need to live in a region cardioprotectet or you need a DEA portatil unit and good information on how to use.