arduino programming for heart rate analysing

Using Arduino Programming Questions
6

Your counts are so high because you continue to add to the counts whilst the sensor value remains high.

Try something like this (untested)

long measurementStartTime = 0;
int beats = 0;
byte sensorPin = A0;
int currentSensorValue;
boolean counted = false;

void setup() 
{
  Serial.begin(9600);
  pinMode(sensorPin, INPUT);
}

void loop() 
{
  if ((millis() - measurementStartTime > 10000) && (beats > 0))  //time is up
  {
    Serial.print("Beats read in 6 seconds : ");
    Serial.println(beats);
    measurementStartTime = millis();
    beats = 0;
  }
  currentSensorValue = analogRead(sensorPin);
  if (currentSensorValue > 156 && counted == false)
  {
    beats++;
    counted = true;  
  }
  else if (currentSensorValue < 146)
  {
    counted = false; 
  }
}

NOTE - the tests deliberately do not use the same value to allow some tolerance as the signal changes from high to low and vice versa but may need adjusting.