The heart has several valves, leaking, or I believe it is commonly known as regurgitation, occurs when a valve seal is less than perfect. But this forum is populated by various members with less than perfect aspects to our hearts, such as arrhythmias or dysrrhythmias. Fortunately for all of us, perfect conditions don't need to exist to be reasonably healthy.
The valves work like check valves, they permit flow in one direction then close to prevent the blood from returning. Alas, sometimes the seal is less than perfect and regurgitation results. Mitral Valve Prolapse is well known and rather common, and if the prolapse is significant enough, some regurgitation occurs. This type of situation can be visualized on Echo Cardiograms. Did your doctor say which valve?
Sinus tachycardia means that your heart was functioning in a regular rhythm at a rate over 100 beats per minute. Like you said, adrenaline can easily cause it to go above 100, exercise, etc.
Yearly visits are pretty generous, if he wanted to see you every 3 months or every 6 months, it may be because he was afraid something is deteriorating, but yearly, no, those are routine visits and he can check to be sure nothing changed, and I'm betting he doesn't expect any changes.
What made you go to the doctor to begin with?